Translation:We do not know who rents our stores.
Similar to below - my Indonesian friends explain it to me simply as a joining word (in most cases) when you are most commonly describing something, similar to functions of 'which' 'is' 'that is' 'who is' 'was'. As bahasa doesn't use a lot of joining words in the same function English uses them, it kind of emphasis in the bahasa sentence that the two are connected.
a bad example/s is: - the ball is big - bola yang besar - the cat is blue - kucing yang biru - A new car - sebuah mobil yang baru
My experience with messaging with my Indonesian friends (with my basic bahasa) is that they use yang far more than duo lingo does (but they are from kalimantan maybe it is different there than where the editors are from).