Ubuntu - GPU - AMD GPU - Monitor - Manually - Check the GPU VRAM Frequency

cat /sys/class/drm/card0/device/pp_dpm_mclk

returns:

0: 96Mhz *
1: 456Mhz 
2: 772Mhz 
3: 1249Mhz

NOTE: The line with the asterisk is the current VRAM frequency.