Auxiliary information and values describing certain data and the conditions it was measured on are called metadata in Gwyddion. They may include the SPM mode, tip bias, scanning frequency, measurement date and time or user comments.
Metadata are always per-channel. The metadata for the current image, volume or XYZ data can be displayed withcommand in the right-click context menu (in version 2.32 or newer) or using → (in older versions). The browser lists all available metadata as Name, Value pairs. It also enables to modify and delete values or add new ones. It is possible to export all metadata of a channel to a text file with button.
The level of metadata support differs widely between file formats. For file formats that are well documented and/or allow to import all metainformation generically lots of auxiliary data including obscure hardware settings can be listed. On the other hand it is possible that no metadata is imported from your files, for example when they contain no auxiliary data or it is not known how to read it.