I married a Panama women and she left and went back to Panama and wants a divorce.
How do I obtain one when I am in the US

You file for divorce in your state, where you live, and have her served in Panama. You do NOT have to go to Panama to get divorced. If she lived with you in the US for any significant period your court has jurisdiction over her to divide property, assign debt, etc. You can always terminate marital status even if the court lacks personal jurisdiction over an absent spouse.

Having her served in Panama may be problematic, but it can be done.