Un bon diplomate est une personne qui a acquis la technique consistant à laisser à une autre le soin de révéler un secret.

Sentence Discussions French
#1

I think it should be ‘la technique consistante’. Feminine. But am not 100% sure.

#2
English Translation

A good diplomat is a person who practises the technique of letting someone else let the cat out of the bag.

I don’t think the present participle (consistant) is used as an adjective here. So it does not need to agree in gender or number.