There's no such thing, per se, as a 'trader's licence'. There is, of course, a 'street trader's licence' but that's only required by someone who is trading on the public highway (or from premises where people on the public highway can be served).
Assuming that you're not working on (or immediately adjacent to) the public highway, the only permission you'll need will be from the people who own (or who have control over, e.g. by hiring) the premises where you're working.