What do you call a ship that's not in water and therefore cannot be mobilized? For example, if a ship is under repair at a port and is on land, what adjective do you use? I thought about landlocked, but I am not sure if it can be used this way. I usually see it used to describe countries without access to the sea, and while it may be used to describe ships, they probably refer to decommissioned ships.
A ship that has been removed from the water for repair is in dry dock.
To my knowledge, it is not at all common to say that a ship is "landlocked," whether it has been decommissioned or not; as you have noted, "landlocked" commonly describes countries (or states, or what have you) that lack access to the sea. It can also mean "confined to fresh water by some barrier" (as in "landlocked salmon") or "living or located away from the ocean" (as in "a landlocked sailor"), but it would be unusual to use it to describe a ship that has been removed from the water for repair.
If you're asking for a word meaning the ship is not currently on water, perhaps "Ashore" or "Onshore" will do?
Onshore / Ashore: on land, and not on the sea