The correct question tag for the given phrase "Let's go for a walk" is: Let's go for a walk, shall we?

Here's why:

• "Shall we" is the most common and appropriate question tag for an affirmative proposition made with "let's". It suggests a shared intention or invitation and seeks agreement from the listener.
• "Can we" implies seeking permission, which is not be the intended tone for a friendly suggestion like going for a walk.
• "Do we" doesn't accurately convey the meaning of making a suggestion.
• "Don't we" turns the sentence into a negative question, which doesn't align with the positive proposal of going for a walk.