My knee is slightly swelling around knee cap(no redness some pain while walking)for 7 days.if this is fluid, when should this subside on its own? dr?

It Depends: On what is causing the inflammation in the knee. Common causes include trauma, infection, inflammatory arthritis (gout, pseudogout, ra), meniscal tears, arthritis, and other ligament/tendon tears. A thorough physical examination by your internist or orthopaedic surgeon can help narrow down the differential.

10 days: In general, any orthopedic injury (muscles, bones, joints) that doesn't feel a lot better (50% better) in 10 days, should be checked by a physician. Infection can start as swelling so increasing red and pain should be seen asap!