I am wondering if it is possible to typeset two symbols like ^ and ~ over a letter. My idea was something like ^{~{u}}, but it does not work.
Something similar is discussed in: How to typeset the symbol “^” (caret/circumflex/hat)
Unfortunately, only one symbol is explained there.
\~{a}and Zirkumflex as\^{a}, but you can, of course, combine the too:\~{\^{a}}, or simply use a modern LaTeX engine like LuaLaTeX and use the character as is: ẫ.For u there is no precomposed Unicode codepoint, however, and your font might be missing the required glyphs. Expect mixed results.
– Ingmar Mar 24 '22 at 10:35