The S7 diagnostics puffer, as available in ProTool, is not support in WinCC flexible.
Diagnostics messages can be realized in WinCC flexible using the "SFM" (system error messages) function.
SFM is based on the Alarm_S alarm procedure. Here the panel receives significantly more detailed message texts than in the context of the diagnostics buffer.
Furthermore, the SFM messages are send actively (Alarm_S).
In comparison only very few diagnostic messages are actively sent by the CPU from the diagnostics buffer (e.g. CPU in Stop). If all the messages are to be displayed, then the operator must execute the "Read diagnostics buffer" function on the operator panel.
Entry ID 22319131 includes instructions on how to have system error messages of a SIMATIC S7-300 / 400 controller displayed in WinCC flexible.
If messages via SFM in the context of WinCC flexible is not sufficient and you need the S7 diagnostics buffer in addition, then Entry ID 22407622 includes instructions on how you can evaluate the S7 diagnostics buffer using the SFC 51 RDSYSST.
Using the SFC 51 you can output the S7 message numbers and the time stamp on an operator panel.