What is the size of the front axle nut of the Supercycle Hooligan? I was riding my bike one day and saw my font wheel axle nut on the right disappeared. 

I tried to find replacements but none of them fit, I don't know the size of the nut so I cannot find one that fits. I got some nuts that were similar size, but they were 24t so it didn't fit, online people are selling 24t and 26t so I think mine is 26t but I am not sure. 

The bike is a Supercycle Hooligan with 24" tires. Measurements preferred in mm but inches is fine too.

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.
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.