In this question, we are asked to determine which given complex(es) exhibit optical isomerism. Optical isomerism occurs when a compound can exist in two non-superimposable mirror images, often due to chirality in coordination complexes. Let's analyze each option:

1. $[Fe(acac)_3]$:
   • This is a tris-bidentate complex, where acac (acetylacetonate) acts as a bidentate ligand.
   • Such complexes can exhibit chirality if they have an asymmetric coordination environment.
   • In this case, $[Fe(acac)_3]$ can form non-superimposable mirror images, and thus, it exhibits optical isomerism.
2. $cis-[Co(en)_2Cl_2]^+$:
   • The compound contains two ethylenediamine (en) ligands and two chloride ions in a cis arrangement.
   • The presence of chiral centers due to the two bidentate ligands in the cis arrangement causes this to be optically active.
   • Hence, $cis-[Co(en)_2Cl_2]^+$ can exhibit optical isomerism.
3. $trans-[Co(en)_2Cl_2]^+$:
   • In the trans arrangement, the ligands are symmetrical, creating a plane of symmetry.
   • Because of this symmetry, $trans-[Co(en)_2Cl_2]^+$ does not exhibit optical isomerism.
4. $[Co(en)_3]^{3+}$:
   • This complex involves three bidentate en ligands forming a symmetrical octahedral complex.
   • All ligands being equal and arranged symmetrically allows this complex to have chirality.
   • Thus, $[Co(en)_3]^{3+}$ shows optical isomerism.

Based on the above analysis, the complexes that exhibit optical isomerism are $[Fe(acac)_3]$, $cis-[Co(en)_2Cl_2]^+$, and $[Co(en)_3]^{3+}$.