$\begin{array}{l}\text{Here, }\\ \Rightarrow {\left(3^{?}\right)}^{?}\text{= 19683}\\ \\ \text{Putting x at the place of (?)}\\ \\ {\text{So, \hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}3}}^{x\times x}{\text{=(27)}}^{\text{3}}\text{ [}\because {\text{19683=27}}^{\text{3}}\text{]}\\ \\ \Rightarrow {\text{3}}^{x^{\text{2}}}{\text{= 3}}^{\text{9}}\Rightarrow x^{\text{2}}\text{= 9}\\ \\ \Rightarrow x\text{\hspace{0.17em}=}\sqrt{\text{9}}\text{ =3}\end{array}$

Hence, Option E is correct.