الله أعلم means : Allah knows best. Most times people use it when they are answering a question or explaining something that they are not sure about it or they don't know the answer. However, it can also be used after answering a question that the person is sure about it but he uses it as ''a glorification of God'', it's used obviously by the Islamic scholars or ''Sheikhs'' after answering the question they say (هذا و الله أعلم) to indicate that whatever I know, God is the most knowing and he knows best. Hope that was helpful.

1- عندما لاتعرف الإجابة على سؤال ما . 2- عندما تجيب على سؤال ما ولكنك لست متأكداً من الإجابة فإنك تختم الإجابة بقولك والله أعلم

1 ) عنما تقول شيء لست متأكد منه 2 ) عندما يسألك شخص سؤالاً لا تعرف إجابتة

When someone doesn't know the answer to a question, when someone says something that they're not quite sure of, or when a person is interpreting someone's dream, that would be usually a religious man (sheikh) and he'll end his interpretation with "wa Allahu a'lam"

God knows= والله أعلم