Ok,
I'm not sure if you need a licence to take the eggs,
Because I'm in Ireland and we have different rules.
There is no way to check if it's fertile by candling it.
The only way to find out If it's fertile is to,
Crack it open and look for the 'bullseye' or,
Put it in the incubator for a few days to see if anything starts forming,
But as I say check with your local authorities to see if you can actually take a wild duck egg.