If you could go back in time to 1939, would you assassinate Hitler, knowing all the death and destruction he created?

No, 1939 would be too late, he'd already killed millions in Austria and Czechoslovakia by then. His cult of personality was so powerful by that point, that his death would have created a power vacuum at the top of the Nazi party that would have been quickly filled by a dozen others all fighting for their own independent versions of the doctrine; resulting in Nazi splinter groups and dispirit factions - much more deadly and much harder to defeat.

Ideally, I'd make sure he didn't survive his wounds received at the Battle of the Somme in 1916; or failing that the mustard gas attack at Pasewalk in 1918.

No because we defeated him. If we didn't defeat fascism it would have grown within Germany and then someone more insane might have come along and beat us. Beating Hitler was a victory over evil and although many sacrificed their life for it, it made the world a better place in the long term. That war had to happen as an evil ideology was building in the world unchallenged. We didn't just beat hitler. We smashed and destroyed that evil ideology.

Actually, I would rather go back to the early 9th Century Middle England, when Jews became money lenders because of a law passed that meant it was the only job they were allowed to do. (Which is where fascism truly started out of jealousy) To change that law.

That way there would have been no reason to have to have killed anyone.

It wasn't Hitler but all that voted for him as with Trump. Killing him means NOTHING!

Well, I guess i would try to reason with him and tell him about what would happen to him Germany and the rest of the world if he continued on the path he had chosen.

If I had the ability to go back in time I'd go back to a time where he had no power and then do it.

seems like that would destroy reality. loop paradox type of thing, if i kill him, than the new me (if i'm even born) has no reason to time travel to the past.