If you haven't heard of GraphQL, the TLDR is that it's a new way to request data from an API.
One that's easier, faster, better, and stronger than the old RESTful API system.
If you're lucky enough to already grok GraphQL, you'll know the QL stands for Query Language – aka. the language we talk to our GraphQL API in.
It's not a terribly complex language, but you'll still need to do some syntax studying to get the hang of it.
Here are some of my notes from working through Eve's material:
A high-res & printable version of the sketchnote, plus the full course is avaliable here on the GraphQL Query Language page.