@InnesBT This review paper by Gasperini, Tome, and Shendure is pretty good for the biology and protocols you can use for answering questions like this:
https://www.nature.com/articles/s41576-019-0209-0
It covers a lot o protocols and methods (#MPRA, #CRISPR screens, #eQTLs, #scRNA-seq, etc), but it doesn't focus as much on the computational construction of those things.