What is the size of the front axle nut of the Supercycle Hooligan?
The zero-information answer is that you should take the bike to a bike shop. Axle nuts are, as far as I'm aware, a pretty standard size; a bike shop will be able to figure out what size you need and will probably just give you a replacemnt nut. Buy something to make it worth their while.


  Measurements preferred in mm but inches is fine too.


That's not how it works. If it's a metric size, you need a metric size; if it's an Imperial/American size, you need an Imperial/American size. It's not enough to say "Oh, half an inch is about 12mm and however-many threads per inch is about this number of threads per centimetre."


  Btw, if I cannot find any online is it a good idea to 3d print them? I have a 3d printer and I can print in PLA or PETG but not sure if plastic would be a good idea to hold the front wheel in place.


No, no, one hundred times no! Not remotely strong enough.