Answer
$\sqrt{a}$
Work Step by Step
Using $a^{m/n}=\sqrt[n]{a^m}=(\sqrt[n]{a})^m$, the given expression, $
\sqrt[12]{a^{6}}
,$ is equivalent to
\begin{array}{l}\require{cancel}
a^{6/12}
\\\\=
a^{1/2}
\\\\=
\sqrt{a^1}
\\\\=
\sqrt{a}
.\end{array}