How do you know if he wants you to kiss him?

look at him intensley in the eyes on the date, and if he stares at you the same, just lean in.

If it's a girl wanting to know when a boy wants to be kissed:

Most guys will want to be kissed, but if their really into something like a game or something then its not always smart to try kissing him. If your just sitting together then you can basically 99% chance he'll go back at whatever you give him. Even if your walking around you could kiss (don't make out).

If it's a boy wanting to know if a girl wants to be kissed:

They will usually touch your cheek, or rub your arms. They'll cuddle closely to you and put their head near yours. If your really clueless then they might resort to kissing you on the cheek much more then usual.