The compound $\left[Co{\left(N{H}_3\right)}_2\right(en\left)C{l}_2\right]$ can form

The compound $\left[Co{\left(N{H}_3\right)}_2\right(en\left)C{l}_2\right]$ can form optical isomers.

When two compounds have distinct spatial arrangements of the atoms, the same number and types of atoms, bonds (i.e., the connection between atoms), and bonds, but non-superimposable mirror images, they are said to be optical isomers. Enantiomers are any structures that are not superimposable mirror images.

Hence, option C is correct.