Currently, their is little to no info on Snoke. If you want some tidbits about his rise to be the First Order Supreme Leader; read The Last Jedi novelization by the very talented Jason Fry. If you want tidbits on the First Order; read Phasma. Aside from that you may be waiting awhile.....
Bloodline also offers some hints about the First Order and its hidden nature in the years leading up to TFA.
At this point I think we should just have gotten Snoke: A Star Wars Story instead of Solo. The demand is obviously there.
The Phasma book is essential. The Finn and POe stories in Before the Awakening and Bloodline would be worth a look too. The Aftermath trilogy is practically the origin of the FO. Be aware though that these are still pieces of an incomplete puzzle, with no clear indication of when, or if, it will be completed. One thing this set of work convinced me of is that the ST films aren't tapping the full potential of their new adversary.
I have read the majority of the canon material put out so far, and nothing has really taught me anything about Snoke that's not in the movies. It is bizarre that they killed the character without telling us anything about them. They should have put out books already that give us his detailed backstory and motivations, it would have made his death in Episode 8 so much more meaningful.