I was in a car with people and we were smoking weed and we finished smoking and I had no weed on me

I was charged with possession of cannabis and I had no weed on me what is gonna happen in court? none of us had anything on us

You should try but how were you smoking weed if you didn't have any and did the other people get charged?

In court, the person prosecuting the case (prosecutor or police officer) will present what evidence they have that indicates you and your friends had weed in your possession and you will present the evidence that you did not have any. The court will then decide based on that evidence. From your statement that, "we finished smoking," one can assume that you had weed at one time. Whether the court will consider that an admission of guilt will likely be the pivotal issue.