What font does Ubuntu use for really irregular characters like 𠆢, and just general Chinese characters? Since it sort of falls back to a font that does have the glyphs, its impossible to tell where it's coming from. Also, does anyone know of any tools I can use to see what glyphs a *.ttf file supplies (For linux, naturally :P)?
The fallback fonts are decided by Fontconfig; it consults the configuration in
/etc/fonts as well as the glyphs provided by all fonts to determine or decide which particular font is used to provide the character. You can right-click on a character in Character Map to see which font has been used to backfill the character.
Newer versions of GNOME Character Map can restrict display of glyphs to a specific installed font, but you will have to use something like FontForge in order to view available glyphs in a compact format.