Jupiter in the 9th house is usually considered to be an auspicious placement; this is because the 9th house is known as the Bhagya Bhava or the Dharma Bhava. Being a trine house, it is one of the luckiest or most benefic houses in the ascendant (Lagna) chart, so having Jupiter here in a well-placed position suggests that the individual will have the support of luck or destiny in whatever they do.
Since the 9th house governs spiritual learning, pilgrimages, preceptor or teacher/instructor relations, Jupiter well-placed here means that the person might be interested in gaining higher knowledge and may also be spiritually inclined. He/she will follow Dharma very much and also attempt to share his/her knowledge with others happily.
Additionally, if Jupiter is placed in exaltation in the 9th house, meaning that the person is a Scorpio ascendant, then he/she will have a long-lived father as well as good relations with them. Such a person will receive honour from the society in many ways as well as be well-known on the account of their piety and religiousness.
Furthermore, because Jupiter’s 5th aspect would befall the ascendant house or 1st house of the native from the 9th house, it makes sense that their overall life would also be good and they will be protected from many of the dangers that would have otherwise afflicted their lives. Finally, Jupiter’s 9th aspect also falls upon the 5th house of the ascendant chart for the person which would support the individual in terms of speculative investments as well as increase the chances of them having a chaste partner when it comes to relationships and love.
Jupiter in the 9th house cannot be afflicted easily as the only planet capable of truly afflicting Jupiter is Rahu, and the 9th house is the Marana Karaka Sthana for Rahu – much more so if He is placed in an enemy sign or any other sign than one owned by Venus or Saturn. In case of a Jupiter Rahu conjunction, the person will have some weakness in destiny with periodic delays or disruptions, but if Jupiter is exalted or in His own sign (Sagittarius or Pisces), then the effects would be minimized.
Jupiter Ketu conjunction in the 9th house will very likely make a person religious beyond the point of no return unless Mercury, Venus, and Rahu are well-placed. In such cases, the person may consider abandoning their worldly duties and turning into a monk or simply taking up spirituality. I have seen this for three of my clients; two of them had Jupiter Ketu conjunction in the 9th house in Sagittarius and both ended up going to spirituality though one of them was born into a very rich family, and the second one simply became a monk and left all his assets to his brother and preferred to live a simple life while preaching about religion and spirituality.
If Jupiter is placed in the 9th house in Capricorn, His debilitation sign, the person feels weakness in destiny in general; he/she might be someone who feels that things don’t usually work out for him/her. As such, good things take more time than usual and tough times happen far too early or quickly without any prior warning. Their wealth generation is also affected.
Overall, the 9th house is an excellent placement for Jupiter because Jupiter is also the Karaka or significator of the 9th house as well, so He is bound to give good results in the same unless debilitated.