According to the document “Verification of Conformity” for the product the Jolla C2 supports the following 4G bands:
RX:
LTE Band 1: 2110-2170 MHz
LTE Band 3: 1805-1880 MHz
LTE Band 7: 2620-2690 MHz
LTE Band 20: 791-821 MHz
TX:
LTE Band 1: 1920-1980 MHz
LTE Band 3: 1710-1785 MHz
LTE Band 7: 2500-2570 MHz
LTE Band 20: 832-862 MHz