[PRB02-006_p1] - Roronoa Zoro (Premium Booster -The Best- Vol. 2: Alternate Art)

When I use this [Opponent's Turn] effect, can I select a Character that cannot be rested due to an effect as the target of "you may rest 1 of your other Characters instead"?

No, you cannot. If you have no other Characters that can be rested, you will be unable to activate this [Opponent's Turn] effect.