I use bitmoji's in my presentations and they also end up in my canvas pages, quizzes, and other assignments. I save the bitmoji, and then load it as an image in my class files. when I upload it, I'm asked to specify a license type. On the Bitmoji site they really don't specify an attribution method for every bitmoji use.
They say "Are Bitmoji characters copyrighted?
Bitmoji Avatars are only permitted for personal use and they cannot be used commercially. This means you could use one you've made in personal messages or your personal social media. Also, you cannot sell Bitmoji Avatar products – like a vinyl decal of yours or someone else's Bitmoji."
I distribute all my canvas content under a creative commons or fair use license, and feel that while I can't say the bitmoji image is creative commons, it is, for sure fair use, as a non-commercial image... I have been selecting "This material is subject to an exception - fair Use....", but I'm wondering what others select?