When entering riften a guy named maul stops you, at the time I dint care to talk to him... And now i need some info from him can't figure out where in riften he likes to hang out

You can try the keep. However from what I remember of the information he gives you, nothing he says you can't get anywhere else.

I was told I need to speak with him to get info on the thrives guild

Whoever told you this was wrong. As I have posted in other threads (and so has others), you just have to walk to the center of the marketplace to start the guild quest line.

As much as I remember you should try one of the exits from the city that leads to the fishery and some kind of harbor. He is nearby.

Could you elabertate a little? Cause I ran all over the city asking people and nobody told me a damn thing (and yes I was in the market place) I even found them in the rat tunnel and got nothing