PIC32 Configure PPS for SPI CLK
If you look at page 21 of the datasheet, you will see that the row of pins for SCK2 does not have PPS listed for its pin assignments like the other pins do; rather it is connected to either pin 23, 26, 29 or 15 depending on the package. Therefore it is not reassignable.

The SDI2, SDO2, and \$\mathsf{\small \overline{\text{SS2}}}\$ pins are reassignable through the PPS mechanism.