A license is a contract: it can contain any terms or include any requirements, restrictions, etc. which the parties to the contract (i.e. you as licensor and any licensees) mutually agree to. So if people sign a license requiring training, for example, that is legal an enforcable. The key is to put all such terms and requirements right there, in plain language, in the license, so there is no claim that it was not agreed to or disclosed.