Just call up Quest Diagnostics. They have blood drawing centers all over the US. For about $75 they have a doctor to order the test, draw your blood, and run a spike antibody test. That's the test you need to tell if your vaccines are working.

But the vaccines work pretty damned well. I don't think anybody needs to check unless they have immunosuppression like after a transplant or autoimmune disease. Researchers tested vaccinated people who were immunosuppressed after transplants. Many had SARS-COV2 antibodies already. Another bunch did respond well to a third vaccine. The ones with no T-cells at all did not. They would do well if they got Monoclonal Antibody Cocktail at the first sign of infection, but it's not cheap. But transplants are not cheap, either. Maybe saving a transplant patient is worth the cost.

We're flying electric helicopters on Mars yet you can't turn on your clothes dryer in Texas. That's because scientists are in charge of Mars, and Republicans are in charge of Texas.