Translation:What is brighter than your face?
Why is here the construction "lebih ... dari"? I thought it should be used with "daripada".
The meaning or the grammar?
Semantic meanings of sample sentences don't have to make sense. Understanding the grammar is what's most important. So, just take the question literally. (Someone's face is bright/shining, and someone else is asking what thing is brighter than the face.)
As for the grammar, here's a breakdown:
Apa = what, yang = that/which (used for emphasis), lebih = more, terang = bright, dari = than, wajah kamu = your face (literally "face (of) you").
In other words, a literal translation could be: "What is it that is more bright than the face of you?".
I like this answer and agree with what you say about grammar -vs- meaning. Problem is -- when I wrote What is more bright than your face (a literal translation) it was rejected (submitted) :-D