A thought bubble is the usual medium, but there may be examples where a thought bubble is not used but which it's clearly meant to represent a character's internal monologue too.
https://booru.allthefallen.moe/posts/360630 is a good example of the contrast because there is thought bubble apiece for Katara and Aang at the top, but then at the bottom-right you can see Aang having a 2nd followup though.
Here instead of a bubble being used, his thinking is just floating as white text above a glowing picture of himself.
I don't know if this is a very common medium used as an alternative or supplement to thought bubbles. Anyone recognize it from any other art? I don't know if there's a tag for it, would anyone have ideas of what to call this for inventing a tag?