Answer: Segments JL and KL need to be constructed using a straightedge.
Step-by-step explanation:
In the given flowchart, the triangles obtained by line segments JN,NL and NK,LN are ΔJNL and ΔKNL respectively that are proved to be congruent to prove segments JL=KL are congruent but they didn't mentioned to construct segments JL and KL to construct triangles ΔJNL and ΔKNL respectively by using straightedge.
Rest of the proof is correct.
Hence, the only error in this flowchart is "
Segments JL and KL need to be constructed using a straightedge".