how is the principle of popular sovereignty reflected in the declaration of independence or the articles of confederation

In the declaration of independence the introduction already asserts the right of the people to be independent politically and to choose its separation from another people. No mention of a monarch or ruler is made. That is already an indirect statement on popular sovereignty. Then the preamble very explicitly states that the power of the government is derived from the "consent of the governed", i. e. the people. Finally, the conclusion states that the Founding Fathers have made these decisions under the Authority not of a ruler but of "the good People of these Colonies".

This is way more implicit with the Articles of Confederation. Since the Union had already been established the need for explicit and reiterated mentions of the people as holding the authority of the country was not as evident. Expressions such as "general interests ", "free inhabitants" and the "authority to us given" (by the people) are the ways this principle is mentioned.