Here's how to pronounce it:
* Lisa: "LEE-sah"
* del: "del" (like "dell" but with a short "e")
* Giocondo: "joh-KON-doh"
So, the full pronunciation is LEE-sah del joh-KON-doh.
"Gherardini" was Lisa's maiden name, and while it's sometimes used, it's less common than her married name, "del Giocondo."