Dear do27,
I am afraid in ATENA Engineering 2D it is not posssible to directly define a monitoring point for a specific location on a reinforcement bar (in the ATENA-GiD user interface of ATENA Science, it is possible to define a Monitoring point specifically for the reinforcement), however, you may be able to manage to locate your monitoring point for the Stress in Integration Points such that the nearest IP is in the reinforcement (and not some IP in the surrounding material) .

Another solution is to output the Stress values for all reinforcement and filter the point of your interest in a spreadsheet (e.g., using the Reference Coordinates), see ATENA Troubleshooting, 2.2.21 How to get the nodal forces at 100 nodes as output in text-file or other? for more information.

Yet another way to get the desired output is to export the results from Egr 2D (File - Export - Binary Result Files), read them into ATENA Studio (Create new project from result files; see the ATENA Studio User's Manual, 5.1 Processing of Existing Data for more information), then define and extract the corresponding Monitor (4.3.2.2 Monitor Request).

Reagrds.