Snoke mentions that Luke Skywalker, “one of the most formidable Jedi,” began his training on the planet, and when Kylo asks why Snoke refers to Luke with respect, Snoke responds that Luke earned both his respect and fear, and that if Snoke had Luke by his side instead of Kylo, he’d be controlling the galaxy by now.
In a preview for the Snoke one-shot shared by the official Star Wars website, we see him and Kylo Ren, having only recently established their master/apprentice dynamic, landing on Dagobah and traversing through its marshy terrain.