So for a campaign I'm making there is a new type of magic that can do pretty much anything, except for bring people back to life. The most experienced person in this art is with the party, but everyone he knew is dead. I wanted to give the players an opportunity to use a combination of a wisdom and intelligence check to think of a solution. How would I make this into one check?
As I understand it, you are asking how, mechanically, to make a roll that uses two scores - Wisdom and Intelligence.
As far as I know, there is no pre-existing mechanic that does that. Things you can do:
1) Have someone roll wisdom and then roll intelligence (probably with an appropriate skills, depending on what exactly you're doing - history? insight? Investigation? Arcana?), and take whichever is lower (kind of like disadvantage) or whichever is higher (kind of like advantage).
2) Roll both and add them together! Not really supported in any way in the rules, but you can do whatever you want.
3) A sequence of checks - first the players have to find a thing (perception check) and then investigate the thing (investigation check)
Alternately, you can present the problem to the players and then adjudicate what rolls (if any) are necessary for it after they decide what they're doing. Maybe their approach will be to do something totally different, that might not require a check at all! Or might end up being persuasion (charisma) or something else.
I'm trying to make this like "dude is sad cuz his friends are dead. then your dude can think of a loophole to make them not dead. the check is for if you can think of it. (sorry if this makes no sense.read it again)