My son received today a summons for a credit card debt in the sum of almost 2,000 dollars. The problem is that he never have a credit card. How he can provedl this to the collector and the bank that he does not owned that money.

Sounds like his identity was stolen. Same thing happened to my best friend. She began to fight it but the first thing she had to do was get a fraud report and file a police report.
Good luck

File Notice of Intend to Defend with the Court, If you don't they will obtain judgment again you.

Now request the original contract signed to compare signatures, this can be done by Notice to Discovery to the Plaintiff. If they fail to comply you must demand at the hearing they produce the original to comparte signature, since ID theft has most likely occurred.

Check credit report to see what other items are incorrect and file a ID theft with the Police, FTC, and give notice to the three Credit reporting bureaus.

My son received today a summons for a credit card debt in the sum of almost 2,000 dollars. The problem is that he never have a credit card. How he can provedl this to the collector and the bank that he does not owned that money.
In most jurisdictions, the plaintiff ( cc company / bank) bear the entire burden of proving that your sun owes the money claimed. They must provide evidence such a credit card application or sales drafts bearing your son's signature. Your son does not have to prove anything. Is he a victim of identity theft? Has he contacted the Credit Bureau to see if there are other accounts in his name that he may not owe. If the ptff cannot produce proof, he should have not problem.