My neutered dog has "lumps" inhis groin area, does he still have testicles?

A neutered male by definition has had his testicles removed.

How old is your dog? I would suggest taking him to the vet to make certain that he is healthy.

You should get it checked out, but it could also just be his reproductive organs it's more noticeable on some dogs then others. You may notice they get harder if he gets excited. If they seem abnormally large then it could definitely be something more serious.
Did your vet say it was routine surgery? Did he mention anything about a retained testical?
How long has he been nuetered?

Obviously the first thing gto say is go to your vet... we can't diagnose on here, just try and help give you an idea of what to expect from your vet.

I'll just run through a few possibilities as I don't know exactly what you mean by lump in his groin.

There's a difference between neutering and castration.
Castration is when they physically remove the testes clean from the dog (and parts that go with them)
Neutering is when they make an icision in front of the testes and remove everything that way. It's a lot less invasive. My boy still looked like he had full testicles for about a month or so after the surgery then they gradually started shrinking.

Also when males get a little 'frisky' even after neutering you can physically see a lump near the base of their penis.

If the lump is anywhere else then unfortunately there are too many options... it could be a cyst, abcess, bite, tumour, fatty tumour... etc etc