Doomsday is comparable in strength to Superman, who is weaker than Thor. Thanos is quite a bit stronger than Thor and would be stronger than Doomsday as well. But Doomsday is more mobile when he fights, while Thanos is more experienced and a better hand to hand combat fighter. This is extremely difficult to say. Doomsday's ability to destroy the area around him also has to be factored in, but if Superman can withstand it, than I don't see it being a problem for Thanos either.