trying to do monomon

[SourPotatoes]

im trying to kill uumuu and watched tutorials, but theres a wall where you're supposed to enter teachers archives. is there an item i need to get to trigger the wall?

[🉑 rezno[R].technology]

If you mean the area where the Teacher's Archives are situated, then you need to go there from the right side (on the left side is a breakable wall shortcut that you can destroy from the right).

[kanna]

Two areas you can enter the right side of Fog Canyon from are either Fungal Wastes or Forgotten Crossroads. Both paths require an ability you might not have yet. If you're missing the ability in question, you should explore the Royal Waterways more thoroughly first.

If you haven't been to that last location yet, then I suggest you could also pay some attention to Elderbug in Dirtmouth. He gives hints on the best places to go next, based on what you've done so far in the game.