The rules are no different than for PCs. (In fact, the rules for Resting on PHB p. 186 say character, not player character.)

The normal rule is that on a short rest, a character may spend any number of their unspent hit dice to roll them, with their Con modifier applied to each die, to regain that many hit points (up to their normal maximum).

That's how monsters do it too.

So for your cloaker, yes: it can take a short rest to roll any of its unspent 12 hit dice, which are d10s, and for each one its spends to roll, it adds +1 due to its Con modifier.

The rules are no different than for PCs. Though the rules for Resting on PHB p. 186 say character, not creature, these are the only rules in the game for how resting works, so all creatures with effects from resting (such as healing) have to use them.

The normal rule is that on a short rest, a character may spend any number of their unspent hit dice to roll them, with their Con modifier applied to each die, to regain that many hit points (up to their normal maximum).

That's how monsters do it too.

So for your cloaker, yes: it can take a short rest to roll any of its unspent 12 hit dice, which are d10s, and for each one its spends to roll, it adds +1 due to its Con modifier.