Used with a negative verb to mean 'not anywhere' or 'nowhere'. The negative verb is required.
I couldn't find the key anywhere.
Used in affirmative contexts to mean 'everywhere' or 'anywhere'. Often appears with verbs like ある or いる.
The keys are nowhere to be found.
He didn't go anywhere.
Flowers are blooming everywhere in this town.
It's an ordinary story you can find anywhere.
そのお菓子はどこにも売っている。
That snack is sold everywhere.
I don't plan on going anywhere today.
The book I was looking for isn't anywhere to be found.
どこか means 'somewhere' and is used in questions or affirmative statements about an unspecified place, while どこにも requires a negative verb for 'nowhere' or an affirmative one for 'everywhere'.
どこでも means 'anywhere, no matter where' emphasizing lack of restriction, while どこにも focuses on existence or non-existence across all places.
どこも is nearly interchangeable with どこにも, both pairing with negatives for 'nowhere' or affirmatives for 'everywhere', though どこも is slightly more common in casual speech.
all over; everywhere
Compound of どこ (where) + に (particle) + も (inclusive particle). The combination with も gives the sense of 'any' or 'every' depending on context.