can a token exist without its owner card. for example zed making a shadow token

Yes — tokens don't need any owner card to exist. Tokens are their own category of Game Object, not cards (Rule 185), so a Shadow Clone created by Zed, Without a Sound exists on the board purely as a token.

Its "owner" is just defined as whoever controlled the effect that created it (Rule 183), which is Zed's controller — no physical card is required or tracked. The token persists on its own even if Zed later leaves play; the only thing that makes it vanish is being put into a non-board zone other than the Chain (Rule 186.1), e.g. if it's killed into the trash. So a token can't "exist" in your hand, deck, or trash, but on the board it's a fully independent object.