In case of any yoga or planetary combination if any of the yoga planet is weak or debilitated then one building block of the yoga has become weak, and will not give the desired result. The yoga can be in any house if anyhow gets malefic connection like 8th and 12th house then the yoga will not give the result either. A native will enjoy or get the fruitful result of any yoga when the yoga is devoid of all malefic effect and weakness in the horoscope.

In your scenario moon and Jupiter together will definitely give good result if they are fulfilling the above mentioned conditions, otherwise they will give result according to the house lordship combination like other general combinations or conjunctions of planets. Debilitation of a planet means the planet is weak to some extent, but sometimes a debilitated planet acts as very strong planet, that depends on various other factors of the chart. but generally, debilitation will decrease the yoga strength. Normally gajakesari yogas are formed when Jupiter is in kendra house from moon, hence, Jupiter and moon together forms Gajakesri yoga if well placed then also the combination gives good result. Moon is the significator of  planet of mind, kind-hardheartedness, mobility, happiness of any kind or in any kind and prosperity ion life. On the other hand Jupiter is the significator of wealth, knowledge and wisdom, children, fame of any kind, luck (as it  is the lord of 9th house of natural zodiac). a well formed Gajakesari yoga in any horoscope gives the native blessing to enjoy all these aspects of life smoothly.

But, i have seen practically in my practice life that if gajakesari  yoga is present in the chart and the yoga is not strong still people get a little bit result in their dasa antar. Due to the weakness of the yoga sometimes you may not feel any result of gajakesari yoga but at least it will not let you finish completely and will give the sustainability even in the worst situation in life in any dasa anatradasa pratyantar dasa timing…