both: $x_1^k$

long subscript w/ both: $Z_{x+y+z}^j$

long superscript w/ both: $Z_x^{k+j}$

long w/ both: $Z_{x+y+z}^{k+j}$

Wrapped in mrow: $x_1^k$

parts with various heights: $x_n^{\frac{f}{g}}+x_{\frac{f}{g}}^n+{\left(\frac{f}{g}\right)}_n^x$