Diagnostic data are a set of certain parameters that have been present during acquisition. It depends on the instrument, instrument driver version, and acquisition software, which parameters are available and in which format they are stored.
To show diagnostic data that has been stored by OpenLab CDS, use the Samples > Diagnostic data snippet:
If nothing is shown with this snippet, your diagnostic data may have been stored by an older ChemStation version. In this case, use the Samples > ChemStation specific > Diagnostic data snippet instead.