Stock weight is around a 5 wt.
Listed 5 Weights can vary between brands as the chart above shows, so pick a brand and just stick with it.
Personally I like Maxima blue label 85/150. Good quality, local shop keeps it in stock, used it for years when club racing so I just keep using it.
I found the stock tenere fork harsh on small bumps. The fork piston compression holes are tiny and one of the reasons for this. On other bikes I always went up to 7.5 or 10wt to get a bit more compression and rebound damping. I would not do this with the tenere. It will make the harshness worse.
You could always try something lighter to try and help this issue. I got rid of the stock pistons so never had a chance to see if ti helps the issue.
Best advice is to change it often. Should be done at least 1 time/year.