what is banquos thought about macbeth and the crown

thought was o kill duncan for his crown

This really depends where you are referring to. In act 1 scene three, Banquo says "look how our partner's rapt". Macbeth's brain is working overtime as he has just heard the witches' suggestion that he will become king.

Later on in act 3 sc. 1 Banquo muses that Macbeth has indeed killed Duncan for the crown:

Thou hast it now: king, Cawdor, Glamis, all,

As the weird women promised, and, I fear,

Thou play'dst most foully for't:

In both cases, Banquo has suspisions about his friend's obsession for the crown.