KATHOPNISHADA CHAPTER 1- SHLOKA 23

                                                         शतायुषः पुत्रपौत्रान्वृणीष्वा

                                                       बहून्पशून् हस्तिहिरण्यमश्वान् ।

                                                          भूमेर्महदायतनं वृणीष्व

                                                       च जीव शरदोयावदिच्छसि ॥ 23

                             SHATAYUSHAH PUTRA PAUTRAN VRUNISHVA

                             BAHUM PASHUN HASTI HIRANYAM ASHWAN |

                               BHUMER MAHAD AYATANAM VRUNISHVA

                             SWAYAM CH JIV SHARADO YAVAD ICHHASI ||23

(YAMA SAID) ASK FOR SONS  AND GRANDSONS WHO MAY LIVE FOR HUNDREDS OF YEARS  AND HEARD OF CASTLES ,ELEPHANTS  AND HORSES .CHOOSE THE ENTIRE  EARTH TO BE YOUR RESIDENCE FOR AS MANY AUTUMNS AS YOU WISH ||23

   This is also continuation of God of Death telling Nachiketa to ask for something else , other  than
KNOWLEDGE of what happens after Death.I think what is implied in theses Shlokas is that at every stage of our life we have a choice  and most of us make MORTAL choices. There are 4 Purusharth ARTH -KAMA -DKARMAND MOKSHA . Moksha is the last one . The ARTH IS MAKING MONEY, KAMA IS FULFILLING DESIRES ,DHARMA IS DOING OUT DESIGNATED DUTIES  AND MOKSHA IS ETERNITY .
  I do not need to explain on making money. The Kama is not SEX as many think die to various reasons - KAMADEV God of sex, Kamasutra  describing various ways of making physical love  etc . But there is broader meaning of Kama . One that makes our sense organs happy would be the better meaning . So it may be sex or eating or drinking or listening to music etc The Dharma means our duties . In this life we have different Duties - such as son or daughter  brother or sister, husband or wife - these ar at personal levels in our family. But in our outside world , we have duties as neighbor, friend, employees or employer, citizen etc. We also have some duties towards the society .But in addition to these duties the Dharma also means to DO THINGS WHICH ARE MORALS . Making money or having a marriage or  having sex - as long as it is done morally , we are OK
    So in this Shloka the God of Death is asking Nachiketa to ask for any of these as most of us STOP t that levels only . Achieving NIRVAN or Moksha is like climbing a ladder . There are steps  and by climbing on these rungs we get closure to the Mokasha . But most of us get entangled at lower levels of ARTH -KAMA AND MAY BE DHARM . So he is offering all the temptations that we all fall for most of the times in most of our lives.
    So in short He is offering the temptations to see how firm the student -Nachiketa - in his desire to KNOW.

KATHOPNISHADA CHAPTER 1 SHLOKA-22

                 
                                                  देवैरत्रापि विचिकित्सितं किल त्वं

                                                         च मृत्योयन्न सुज्ञेयमात्थ ।

                                                   वक्ता चास्य त्वादृगन्यो न लभ्यो

                                                   नान्योवरस्तुल्य एतस्य कश्चित् ॥ २२

                                  DEVAIR ATRAPI VICHIKITSIAM KIL TVAM

                                   CHA MRUTYO YANNA SUVIDYEAM AATTHAM |

                                   VAKTA CHA ASYA TVADRG ANYO NA LABHYO

                                  NANYO VARASTULYA ETASYA KASCHIT ||22

               OH GOD OF DEATH, YOU SAY THAT EVEN GODS HAVE DOUBTS

ABOUT THIS (QUESTION), SO WOULD BE BETTER TO TELL THAN YOU (ABOUT THIS)

AND NO OTHER BOON CAN BE EQUAL TO THIS (ANSWERING MY QUESTION) -22

         This is simple one  and not much can be added to the straight meaning . Nachiket was tempted by Yam to ask for something else, but he does not want anything else  and wants the answer . Lord of death - YAMA will be the best or mos suitable person to answer as to what happens after death.So Nachiket is insisting though politely that Yama should teach him as to what happens after death and he does not want any other boon . 

KATHOPNISHAD CHAPTER 1 SHLOKA -21

               
                                                     देवैरत्रापि विचिकित्सितं पुरा
     
                                                      न हि सुविज्ञेयमणुरेष धर्मः ।

                                                      अन्यं वरं नचिकेतोवृणीष्व

                                                     मा मोपरोत्सीरति मा सृजैनम् ॥ २1
                                 
                                      DEVE ATRAPI VICHKITSITAM POORA

                                 NA HI SUVDHYEYAMANURESH DHARMH

                               ANYAM VARAM NACHIKETO VRUNISHWA

                                  MA MA UPAROTSI R MA SRUJAINAM ||21

EVEN THE GODS HAVE DOUBTS ON THIS (TOPIC) AS IT IS NOT EASY TO UNDERSTAND

                   BEING SUBTLE, OH NACHIKETA CHOOSE ANOTHER BOON,

                            DO NOT PRESS ME ON THIS, GIVE UP THIS ONE ||21

         This is a straight forward Shloka.
         Nachiket asked to know about life after death  and so it is a subject where many and most will not be interested or understand or appreciate . It will put most of us to sleep. So the Yama wants to make sure that the student is anxious enough to KNOW. Many of have questions , but we do not have ability or patients or time to really make efforts for the reaching higher levels. We all have seen this in our life. We attend spiritual lectures  and gave questions , but we do not work for it - practicing YAMA, NIYAMA, MEDITATIONS etc . We all want instant satisfaction. So Lord of Death wants to make sure that Nachiket , the mortal is READY for the discourse. Even in Ganapati Atharvshirsh,it is stated that Do not give this Stotra to wrong student.
       It is also possible that Yama wants to make sure that Nachiket HAS INTENSE DESIRE CALLED ART IN SANSKRIT, There is story . There was a teacher who had a student who was not following usual regular practices to achieve the highest levels of Samadhi. He was asking the teacher as when will he see the God . One day the teacher went to to a river for bathing  and doing morning prayers. The student accompanied him and had the same question. The teacher  and the student were in the waters . The teacher pressed the head of the student under water . The student started struggling  and the teacher continued to press it down . After short time , the teacher allowed him to get his head out of water  and breath. The student was surprised and asked teacher as to why did he do this. The teacher answered, "When his desire to see GOD would be as intense as was to breath under water , he will see God."

KATHOPNISHADA CHAPTER 1 SHLOKAS- 20

                                                      येयं प्रेतेविचिकित्सा मनुष्येऽ

                                                       अस्तित्वे के नायमस्तीति चैके ।

                                                         एतद्विद्यामनुशिष्टस्त्वयाऽहं

                                                         वराणामेष वरस्तृतीयः ॥ २0

                                        YEYAM  PRETE VICHIITSA MANUSHYE

                                        ASTI ITI EKE NA AYAM ASTI ITI CHEKE |

                                              ETAT VIDYA ANISHISHTA TWAYA

                                             AHAM VARANAMESH VAR TRUTIY || 20

THERE IS DISCUSSION WHEN MAN (LIVING)DIES , SOME SAY HE IS THERE AND SOME 
      SAY IS NOT THERE .AS MY THIRD BOON I WOULD LIKE YOU KNOW FROM YOU||20

   This the REAL question that will be answered in this UPANISHADA. What happens after the so called death of the physical body . No one thinks that dead body is a alive person . The discussion that occurs among the people that are still living physically as to when some one dies is ANYTHING left. As one can imagine there are various thoughts about life after death. Some feel this is it . There is no existence after physical body dies . On the other hand many believe that there is after life. The Vedic religion has reincarnation and other Abrahamic religions - Christianity , Judaism and Muslim religion have different thought process about existence after the death of physical body . The Atheist  do not believe in life after death.  So Nachiketa is asking his third boon and wants to know about the life after death  and who could be the best teacher ,none other than God of Death - the YAMA.
   There are many thoughts about the after life  and we don't need to discuss them here . But something else to note is that Nachiketa has asked his Boon in order of what WE SHOULD behave  In the first boon he asked for his family -he wanted to see his father happy ,In the second boon he asked for the welfare of the general public and when that is done then only he asked for the HIMSELF.