Is it possible for Goku to use the Spirit Bomb in the Tournament of Power? Well, the answer is a simple yes, but let me explain to you how this is possible. First of all, the reason many fans believe that Goku cannot use the Spirit Bomb is because the tournament is being held in a lifeless void. That might be true in a way, however; that doesn't make it impossible to use the attack.
Remember that Goku needs to borrow the energy of his surrounding life forms, even nurture itself, in order to charge the Spirit Bomb. Using nature is out of the question in the Tournament, however; borrowing others powers is not. Goku will still have the other members of Universe 7 that he can gather energy from. As a result, this means that Goku will be able to use the Spirit Bomb.
However, does this mean that it will be weaker than the one he used against Kid Buu, as there will be fewer options gather energy from? Not exactly, as Goku might be able to gather the power of someone, who will surely have enough strength to beat Jiren.
Remember, Beerus who is Universe 7's God of Destruction doesn't want to be erased and might be allowed to send his energy to Goku. As fans got to see a few weeks ago, as long as both Zeno's are entertained, the rules can be bent a little. That means that if the Zeno's find the Spirit Bomb to be entertaining, they may allow Beerus to share his energy, as they allowed Master Roshi to use his sealing bottle.
If this was to happen, Goku would have the power of both Kai's, Beerus, Gohan, Vegeta, Krillin, Piccolo, Tien, Freeza, Master Roshi, as well as both Androids 17 and 18 to take power from. This power might make the Spirit Bomb strong enough to take out someone like Jiren, if Goku does choose to use it.
Dragon Ball Super's "Universal Survival" saga is part of the recent simulcast agreement that sites like Crunchyroll and Funimation have scored. Dragon Ball Super airs on Crunchyroll Saturdays at 7:15 p.m. CST, and Toonami airs the English dub on Adult Swim Saturdays at 11:30 p.m.