- Check user's person doc, administration tab. On that tab is ther version of Lotus Notes installed on each workstation used by the person.
- Check person doc
- Check session.NotesVersion property
As Outside Code w/o access to Domino via (web service or COM):
- check registry for latest version installed (could be multiple versions of Lotus Notes installed on a workstation)
- check ID 1 version tag / property in nstrings.dll (There are also the product name and product version tags, too.)