Mild medial joint space narrowing (if at all), no major osteophytes (bone spurs), no effusion. So little to no arthritis. No major abnormalities. Looks like a healthy knee. Sunrise/merchant view would be helpful to look at your patellofemoral joint. Are stairs your problem or prolonged kneeling? If so, then patellofemoral joint arthrosis. If you have locking/catching/clicking and pain on the inside/medial of your knee then likely meniscus tear. If the pain is bad enough, I'd see your PCP who can get an MRI to rule out other things such as meniscus, ACL, OCD lesions, PVNS, etc. Try nsaids, home pt, quad stretching/strengthening.
Same image, better quality