Any way to see AI level in-game?

On the foreign relations screen. Go to the stats tab, I believe it is under Misc.

There is a known issue with difficulty level resetting. It started happening to me recently even though it hadn't happened before. Pressing CNTRL+N triggers it.
I updated to latest patch which seems to have fixed it.

DA is correct about the listing of the AI intelligence level in the foreign relations screen, however, this is not quite the same as the difficulty level (i.e. AI intelligence = Ultimate -> Difficulty = Suicidal). See the Wiki Difficulty Level article for the magic decoder ring between AI intelligence and Difficulty. Note that the difficulty level is defined by the lowest AI intelligence in the game. Also if relations are set to anything except unknown the difficulty level may be recorded as less than you selected (my first suicidal game only counted as masochistic because I set relations to 'known').

Mystikmind is also correct about ctrl-N being a cause of a sudden unexplained loss of AI intelligence. He mentioned that this is fixed in the latest patch which is something I have no knowledge about one way or the other. In any case it's really no big deal since ctrl-N only saves you a click or two. If you feel the need to use ctrl-N you may as well just go back to the main screen and start a new game. Then you're guaranteed not to see this issue.

I'm on the latest patch and the Terrans are the only one I've noticed dropping intelligence after a ctrl+n. I was playing around testing a strat with random opponents and the terrans had popped up on a map regeneration. They lagged well behind, so I took a look and sure enough they were back down a notch from the other AI. So you still have to keep an eye on them if they're in the game and you ctrl+n.

Actually i do not know if it is an official fix in the latest patch? All i know is that my game never used to reset AI intelligence until recently when it suddenly started doing it. Then when i installed the latest patch it stopped doing it, that's all i know!

As for going back to the main screen to start a new game, sounds easy, but that is a severe pain in the ass if you have to keep doing it allot - especially if your looking for a particular map geography in order to try a new strategy/experiment or somthing.

Thanks everyone. I'll check it out on the Foreign Relations screen and restart if necessary

Cheers!