Here's how you could approach it:
* If it's a misspelling of "Gaspar," it would be pronounced like "GAS-par."
* If it's a made-up name or a variation of a foreign name, you could try to sound it out phonetically. For example, "gee-AS-par" or "ge-SPAR."
Ultimately, the best way to know how to pronounce it is to ask the person who uses the name or to see if it's listed in a pronunciation dictionary.