What kind of taxes is a G4 visa holder exemption of? And how can that holder ask for return them?

A G-4 visa holder is exempt from ALL taxes on income earned in his primary job.

He MAY be liable for taxes on stock transactions, however; it depends on the tax treaty between the U.S. and his home country.

If the spouse of the primary G-4 visaholder gets permission to work and does so, that salary is fully taxable.

But does the spouse of the primary G-4 visaholder need to pay social security taxes? He/she will not be able to receive any benefits.

Yes, the spouse must pay Social Security taxes even if tgey stand little chance of qualifying for benefits.

No one says tax policy is fair.