I'm playing tutu and for a monk it says a monk's fist becomes a +3 weapon my question is will that work would i run into a enemy i could not hit?

yes read it as +3 weapon for what you can hit

I understood his question as "is there an enemy that i cant hit even with my +3 fists".

Unfortunately, I have little knowledge about BG2. But for sure you can hit anything in BG1 with that.

Yes, there are a few enemies in BG2 that require a +4 or better weapon to hit. But emphasis on "few."

Specifically, Demi-liches (of which there's 1 in the original game and 1 in the expansion) require a +4 or better weapon to hit.

I'm unaware of any other foes in the game that require this, though.

The Improved Mantle spell will also block the +3 fist, requiring at least a +4 weapon. I seem to recall a few mages using that one, but it has a very short duration.

There's also Mariliths, The Ravager and Damogorgon.

I didn't know about the Mariliths, but I should've remembered the other two. Good to know.

Also, I believe your fists, assuming your level is high enough for them to count as magical, will not work on:
* Magical golems
* Enemies protected by "Protection from Magic Weapons"

(Note that magical golems will only appear in Throne of Bhaal (including Watcher's Keep.)

Edit: There's also the guy in the Baldur's Gate 2 tutorial, who (IIRC) can't be hit by *any* weapon regardless of bonus. Fortunately, you are not supposed to actually fight him (and if you do somehow manage to kill him, it becomes impossible to escape the tutorial).

I think the werewolf island quest in BG:ToSC requires you to kill a few monsters that need a +3 weapon to be able to hurt them and there are only 3 weapons that count as at least that strong

Plus 3 or silver: Werebane (dagger) or Sword of Balduran (bastard sword).