Translation:I wonder what he did in the seventies.
In this case they don't have exactly the same meaning, I am wondering means, I am pondering, I am meditating on. I wonder means simply, I'd like to know, or it would be interesting to find out.
You turned it into a question. It'd be something like; I wonder: What did he do in the seventies?
You keep the same sentence structure in statements (I wonder what he did in the seventies).
Statement - I don't know what that is
Question - What is that?
There are a few exceptions, but that is the general gist of statements. For example, you'd say something like "there is a cat that is orange"; you wouldn't say "there is a cat that orange is".
I wrote "70-talet" instead of sjuttiotalet. I think it should be accepted as well.