How do you say what's up pumpkin in spanish?

It depends what you mean.

If you are talking to a pumpkin or other similar gourd/squash and you wish to ask it what's up, you could say "?Que te pasa, calabaza?"

If you are using the Word "pumpkin" as a form of endearment (like "honey" or "sweetie"), you will need to use a different one in Spanish since "pumpkin" cannot be interpreted that way. Good replacements include: cariño(a), cielo, miel, mi corazón, etc. Insert your replacement into the blank in this phrase: "?Que te pasa, _____?"