Question

Emma is a leader in (who, whom) we have great confidence.

Answer 1

Ever heard of object of the preposition?
http://www.chompchomp.com/terms/objectofthepreposition.htm
http://www.grammar-monster.com/lessons/prepositions_object_of_a_preposition.htm

Good, now if you read those links you'll know that 'in' is a preposition so the correct word for the sentence would be?

Answer 2

who???

Answer 3

Uh, no...
Did you read the links?

Answer 4

yes

Answer 5

Don't lie, the second link basically gives you your answer, read it please.

Answer 6

After a preposition, use whom not who.
so it's whom?

Answer 7

Correct :-).