To get Titan’s Revenge in Diablo 2: Resurrected, you’re going to need luck, persistence, or most likely both. It’s a unique item, so it drops randomly, and there’s no guaranteed place to get it. But there are certain monsters in certain places on certain difficulty levels that are much more likely to drop it than others.
The monster most likely to drop Titan’s Revenge is Baal on Normal difficulty, so your best bet is to repeatedly defeat him until he drops it. This can get a little boring though, and if you want a more varied (but probably longer) Titan’s Revenge farming experience, then you can try the Secret Cow Level or the whole of Act III on Nightmare difficulty. You could get one on later Acts and higher difficulty too, if Act III Nightmare is too easy for you, but the probability drops slightly. Just don’t waste your time with Acts I to IV on Normal, or Acts I and II on Nightmare.