السلام عليكم ورحمة الله وبركاته أحسن الله إليكم I'm a revert currently staying with my father who has 2 dogs in the house. Often times they touch me but I don't know if their saliva touched me and where. How do I know which spots on my clothes to clean for salah?

You do not clean anything you did not actually see the dog wet (by the saliva), because clothes are pure by default and doubt does not remove that. If you did see it land and then forgot where, you wash the spot you most likely think it is, and the whole garment only when no spot is more likely than another as Imam Ibn Baz has mentioned.