Unfortunately no in Guam.
from https://squareup.com/help/us/en/article/4956-international-availability
"Card payment acceptance with the Square app is currently available in the US, Canada, Japan, and Australia. We currently don’t support payment card processing outside of these countries or in U.S. territories such as Puerto Rico, Guam, the U.S. Virgin Islands, American Samoa, and Northern Mariana Islands. We’re working to bring payments processing to more markets and will share updates"
