Receptors for acetylcholine are located on the

plasma membrane of the target cell

Explanation:

There are two main types of acetylcholine (ACh)receptors:

muscarinic ACh receptors (because muscarin as agonist) which are G-protein coupled receptors that initiate slow response. Mostly, they are located in the central nervous system-CNS (involved in the release of neurotransmitters), heart (control of the heart rate), smooth muscles (contraction).nicotinic ACh receptors (nicotin is agonist) which are  ligand-gated ion channels involved in the fast response. They are located at neuromuscular junctions but also in CNS (involved in synaptic transmission between two neurons).