For a STDL mkv, you can use ffmpeg to grab the first frame and then dovi_tool to extract the rpu and convert to json, in the json can see if the EL is MEL or FEL.
ffmpeg -i filename.mkv -c:v copy -bsf:v hevc_mp4toannexb -frames:v 1 -f hevc - | dovi_tool extract-rpu - -o RPU.bin
dovi_tool export -i RPU.bin -d all=RPU_export.json