Assuming 3 mentions... When “other” was coded as 26, I would have written it this way:

pctin(Q10mention1==26 or Q10mention2==26 or Q10mention3==26,true)

Then, for coded verbs, I usually find that I need to re-base to all. So I would have changed it to this:

pctin(ifnull(Q10mention1==26 or Q10mention2==26 or Q10mention3==26,false),true)

But if ‘Other’ is multiple values, it will complicate the formula to something like this:

pctin(
  in(Q10mention1,26,27,28) or
  in(Q10mention2,26,27,28) or
  in(Q10mention3,26,27,28)
,true)

And if you need to re-base to all, it would be this:

pctin(
  ifnull(
    in(Q10mention1,26,27,28) or
    in(Q10mention2,26,27,28) or
    in(Q10mention3,26,27,28)
  ,false)
,true)