Ⱨⱨ, Ⱪⱪ, and Ⱬⱬ were used in the New Script for Uyghur (Uyƣur Yəngi Yəziⱪ), which was in use 1965-1982. Before Uyƣur Yəngi Yəziⱪ, Uyghur was written with a Cyrillic script (Uyghur Siril Yëziqi) and these letters were simply borrowed from it. Ꞑꞑ was used in Jaꞑalif, a Latin alphabet for Tatar which was in use 1928-1939.
There is no modifying or combining diacritic; there are only precomposed characters with descenders. Note that letters with descenders may be confused with same looking Cyrillic characters, which have different code points.
Descender in Unicode
|Latin Capital Letter H With Descender||Latin Small Letter H With Descender||Latin Capital Letter K With Descender||Latin Small Letter K With Descender||Latin Capital Letter N With Descender||Latin Small Letter N With Descender||Latin Capital Letter Z With Descender||Latin Small Letter Z With Descender|
Descender in Natlangs
|Alphabet extension||Uyghur (New Script)||Ⱨⱨ /h~ɦ/, Ⱪⱪ /q/, Ⱬⱬ /ʒ/||Hh, Kk, and Zz without descenders stand for /χ k z/.|
|Tatar (Jaꞑalif orthography)||Ꞑꞑ /ŋ/||This letter is sometimes replaced by Ņņ.|
- Uyghur New Script at Wikipedia.
- K with descender at Wikipedia.
- Yañalif at Wikipedia.
- Uyghur New Script and Uyghur language, both at Wikipedia.