Which Avengers have ability to kill Thanos?
In comics there are many characters who can and has killed Thanos(most notably ‘Adam Warlock' . Thanos shares some special relation with him afterall). But if you are talking about MCU, there are only four Avengers characters who can go one and one and kill Thanos.
- Thor - After creating Stormbreaker, his powers have been amplified and in the end of the movie ‘Infinity War', He actually killed Thanos even with infinity gauntlet, it's just He executed his plan even at the last moment of his life ....that's Thanos my friend .... Thanos has my respect. But so is Thor. Even after loosing everything, He still didn't break down and fought for his people and the Universe. A hero with such indomitable will, deserves respect of everyone and eligibles as killer of Thanos .
- Scarlet Witch - Incredibly Powerful, stopped Thanos even with five infinity stones without any weapon or augmentation. Pretty sure, if it would be normal Thanos without gauntlet, he would be dead by now. She got the same strong willpower as Thanos, made same hard decision like Thanos, which requires strongest will; She definitely deserves to be respected.
3. Dr. Strange - He is the only man, even Thanos can not calculate. Though never mentioned in the movie,but if you look in details, it is true. That's why, Thanos has to go brutal way, using sheer strength and power of infinity stone at the same moment, to deal with him. Remember the scene when Thanos says ‘no magic', even Thanos respects him, because He became aware of Strange's incredible mystical abilities after their small confrontation. Strange is the only one who knows the actual outcome of infinity war. That's why he didn't used any lethal attack unlike the former two. But it is clear, He definitely has some mystical trick under his sleeves that could be lethal for Thanos.
4. Iron Man - A genious with no superpowers made A Godlike being with additional near God powers bleed - yeah, that's Iron Man! The one and only! A genius like this who is also ‘cursed with knowledge' can kill Thanos; Even Thanos knows that. It is the reason why Thanos ‘respects' him.
Hulk - MCU in recent times made him a joke but if the incredible hulk that defeated Abomination,returns; I am sure, the scenario would be different
Captain Marvel - ?? ( can't say anything except MCU and fans made her God already)
Adam Warlock - Thanks to Mr. Gunn, he will not be introduced for now. But comic fans know , How much important the ‘ULTIMATE AVENGER' is, if we are talking about infinity war and specially Thanos.