1.
anywhere is fine, I don't mind where
A casual expression indicating that the speaker has no preference about location. Often used when asked to choose a place for eating, meeting, etc.
どこでもいい is composed of どこ (where) + でも (even/any) + いい (good/fine). The pattern 〜でもいい means "any ~ is fine" and is highly productive.
Related patterns
Cultural note
Answering どこでもいい to "where should we eat?" is extremely common but can frustrate the person asking, since it puts the burden of decision on them. Japanese social media and comedy often joke about the difficulty of planning with someone who always says どこでもいい.