\documentclass{article}
\usepackage{accents}
\DeclareMathAccent{\wtilde}{\mathord}{largesymbols}{"65}
\begin{document}
\[ \ring{x},\qquad
   \accentset{\star}{d},\qquad
   \accentset{\diamond}{h},\qquad
   \tilde{\accentset{\circ}{\phi}} \]
\[ \dddot{f},\qquad \ddddot{f} \]
\[ \underaccent{\hat}{x},\qquad
   \underaccent{\bar}{\gamma},\qquad
   \underaccent{\triangleright}{q},\qquad
   \underaccent{\tilde}{\mathcal{A}} \]
\[ \underaccent{\wtilde}{V} \]
\[ \undertilde{CV} \]
\[ \hat{\hat{\mathcal{A}}} \]
$\mathbf{\hat{\hat h}}$ gets the bold accent;
$\hat{\hat{\mathbf{h}}}$ not.
\end{document}