GAP Manual: 48.35. ClassRootsCharTable

ClassRootsCharTable( tbl )

returns a list of the classes of all nontrivial p--th roots of the classes of tbl where for each class, p runs over the prime divisors of the representative order.

    gap> ClassRootsCharTable(L3_2);
    [ [ 2, 3, 5, 6 ], [ 4 ], [  ], [  ], [  ], [  ] ]

This information is found by looking at the powermap of tbl, too.