The sentence with the correctly placed commas is:
"President Obama, who was our 44th president, spoke about voting rights."
The other sentences have incorrect comma placements:
- "President Obama, spoke about voting rights, when he was our 44th president." (Unnecessary comma after "Obama.")
- "One of President Obama's speeches, was about voting rights." (Unnecessary comma after "speeches.")
- "Voting rights, were addressed in a speech, by President Obama." (Unnecessary commas after "rights" and "speech.")