Nouns like trigger, fulfiller, satisfier all have problems as words to describe x in the question “Is object x of type Integer?” or in similar questions. In the question as just shown, x is a formal argument or formal parameter that stands for a name or value to be filled in whenever the question is instanced.
In a specific question instance, where x has been replaced with some object or an object identifier, then the candidate object or its identifier might be called a solution (as previously suggested) if it obviously satisfied the predicate, or might be called a candidate or a putative solution or proposed solution if it's less obvious.
In the somewhat-analogous case of molecular docking, the following terminology is used:
Receptor or host or lock – The "receiving" molecule, most commonly a protein or other biopolymer.
Ligand or guest or key – The complementary partner molecule which binds to the receptor.
By analogy, one might refer to predicates as receptors, hosts, or locks, and to corresponding candidates as ligands, guests, or keys. Extending the analogy slightly, a candidate might be referred to as a supplicant.