Agnostics question whether there is a God. They don't believe in organized religion.
The Buddha said that it was not necessary to believe in a god to achieve enlightenment. He neither disputed nor acknowledged the existence of gods, but left it to his followers whether to believe in them. Having said that, many Buddhist sects are now firmly theistic.
There are no agnostic religions. Buddhism, technically speaking, is not a religion; it is a way of life. The Buddha is not a god in the sense that westerners think of god. The Buddha is one who achieved enlightenment.