I kinda wanna do a collab with someone on the wiki but idk how to ask someone to do a collab, how to stay in contact so we can swap drafts, and other basic stuff like that.
I can't speak for everyone, but I've found that the best way to attract collaborators is to have a fun concept or idea to start with. I've co-authored eight SCP articles, and all of them came about because either I really liked an idea someone else had or someone else really liked an idea I had, and we were willing to work together to get it made into a mainsite piece.
In regards to staying in contact, wikidot PM works fine, though I like to keep writing notes all in one place so I'd have a collaboration sandbox page set up with the co-authors' names in the title. Multiple tabs helps a lot, since we'd have three tabs: one for notes we both make as we work on the piece, one for brainstorming and narrative conceptualization, one for the actual in-progress draft. By sharing a sandbox, you don't need to be copy-pasting drafts into messages.
Bottom line is, though, collaborations should be fun for everyone involved! Be polite about asking, put in the effort that's needed, and give credit where it's due. Decide from the beginning who will post the page and have a plan handy for how you'll divvy up the work during the drafting and editing phases.