SQL group by multiple columns
A solution that work in most DBMS is to use a union:

 select loc_a as location, Score, Possible_Score from T
 union all
 select loc_b as location, Score, Possible_Score from T
 union all
 select loc_c as location, Score, Possible_Score from T


Now you can sum that up as:

select location, sum(score), sum(possible_score)
from (
     select loc_a as location, Score, Possible_Score from T
     union all
     select loc_b as location, Score, Possible_Score from T
     union all
     select loc_c as location, Score, Possible_Score from T
) as TT
group by location;


If your DBMS supports LATERAL JOIN you can do something like:

select x.location, sum(x.score), sum(x.possible_score)
from T
cross join lateral (
    values (T.loc_a, T.score, T.possible_score)
         , (T.loc_b, T.score, T.possible_score)
         , (T.loc_c, T.score, T.possible_score)
) X (location, score, possible_score)
group by x.location;


LATERAL makes it possible to reference T in X, so we can use X to normalize location.