What spells affect Planeswalkers in MTG?
There are a ton of such spells, in several categories. A spell might affect (or target):


any permanent (e.g. search for "target permament")
nonland permanents, noncreature permanents, etc (e.g. search for "target nonland permanent")
just planeswalkers, but this is rare (and there are things that say "target creature or planeswalker", so it's a little trickier to search for - this works, but has false positives)


Along with those searches, you can also search for things like "all nonland permanents" to find plenty of things that don't target.

And if a source you control deals non-combat damage to an opponent, you can redirect that damage to a planeswalker they control.