Can anyone tell me what the best move sets for this guy would be
Best moveset would be the double rock one, but that hasn't been available since early 2017. Legacy moveset that's very valuable.
Other than that, depends on what you're using it for. Against the birds (now gone), rock charged move is best, water is fair. Or check out the game press page for Omastar, and get the whole story from the source.
His best moves (Rock throw/rock blast) are legacy.
For current movesets, you want water gun with either Hydropump or rock blast, depending on the role he fills.
Hydopump is best in terms of DPS. He has a lot of competition as a water attacker, though his resistance profile makes him a compelling option.
Rock blast gets weather boost more frequently in most areas, which puts it ahead of hydropump. The flying legendaries all have a weakness or double weakness to rock.
Ancient power is suboptimal, but the 'x' rating on GP is a bit harsh.
Hey, I noticed you regularly ask for advice for a pokemon moveset. I hope I'm not being rude here, but instead of asking here for movesets for every decent pokémon you get, I suggest you check this very site's pokemon pages. Every pokémon has its own page and all of its movesets are listed and graded. There are also explanations about why this or that moveset got this grade. Here is the list: https://pokemongo.gamepress.gg/pokemon-list. Most of what we would say to you is what you can read in these pages already.
Of course, if you have a doubt, if you are not understanding the grading system or if you are questioning some gradings, we will be happy to discuss and help. But I would like to suggest, and I hope I am doing this kindly, that you look a bit for yourself first.
