I have some truetype fonts which support UTF-8 characters. I can use "fc-list" to find certain font. How can I check all available characters in some font? Such as how many characters supported in "AR PL New Sung ExtB".
You could use a different commandline tool,
This should get you the number of glyphs. You'll possibly see up to four different numbers, if the TTF is in some way b0rken. Sane TTF will return identical numbers for all three entries, in which case you may be pretty confident that you got the correct number: