The oxidation state of Cl is ClO₄^- ion is +7. It is the maximum oxidation state which it can have. It is the maximum oxidation state which it can have. It can decrease the same by undergoing reduction and not increase it anymore hence ClO₄^- ion does not undergo disproportionation reactions.

Can ClO4 exhibit disproportionation reaction?

ClO4^- does not show disproportionation reaction.

Which does not undergo disproportionation reaction?

Out of the above species, ClO₄^- does not undergo disproportionation since in this oxoanion chlorine is already present in the highest oxidation state of +7 and hence cannot be further oxidised.