Can you tell mewhy did you not speakthe truth?

This correction is related to the Embedded question. An embedded question is a question that is included inside another question or statement. such as: Do you know where he is?
In this type of question, the auxiliary verb, in the main question, generally appears after the subject.
Look at the example, it is not where is he? But where he is?
Go for details: https://continuingstudies.uvic.ca/elc/studyzone/410/grammar/410-embedded-questions