Sometimes English speakers use the phrase "Let me ask you this:" to introduce a question. For example:
Let me ask you this: where do you see yourself in five years?
You usually use this phrase when you're trying to convince someone of something, or come up with a solution to a problem.
Here's a short example of a conversation:
A: I've been really low energy lately. I don't know why.
B: Hmm. Well, let me ask you this: have you been drinking a lot? Because that's something that will definitely sap your energy.
In this example, Person B is trying to solve the problem of why Person A is low energy.