I am now using UAVCAN ESC (holybro Kotleta 20) on F450 QuadCopter and I am wondering if I can receive RPM data through Sapog Firmware
You need to subscribe to uavcan.equipment.esc.Status as described in the reference manual:
https://files.zubax.com/products/io.px4.sapog/Sapog_v2_Reference_Manual.pdf