I have a general license but I do not know when it expires, please help.
For the United States, the FCC has an online license search function, currently at: https://wireless2.fcc.gov/UlsApp/UlsSearch/searchLicense.jsp
You can choose to type in your call sign to look it up, or if you don't know your call sign, you can look up by name.
The expiration date may be on the paper copy of your license.
If you lost your paper copy, you simply can do a Google search (or other search engine search) for your callsign + "FCC". For a U.S. license, that will usually find the wireless2.FCC.gov web site with information on when the license with that callsign was issued plus its expiration date (assuming its still valid).
If you are not licensed in the U.S., replace "FCC" with the governmental licensing entity (or an appropriate abbreviation) in your jurisdiction, which will work if its records are public.