Im assuming you wear clothes to work, but even with clothes i understand how dirty a body can get while working in dirty environments. I work in a very dirty warehouse and a yard where there is constant dirt, dust, pollution, etc. In the right light you can see dirt just settling in midair. How old are you and how long have you worked there? What types of clogged pores do you have that you can push out on your face? Have you always had clogged pores issues on your face and now its spreading to your entire body? I think dirty environments do not help clogged pores because of how dirty your skin feels and how unnatural it is. I think that they can attribute to attaining clogged pores, mostly blackheads though. From experience I believe that clogged pores are mostly internal issues (hormones), where over production of the oil glands causes pores to create a root deep in your skin. The root then creates hard pus which gets trapped causing a clogged pore. Blackheads are clogged pores with the surface of the skin open. Whiteheads are clogged pores with the surface of the skin being closed. Blackheads are easier to deal with then whiteheads because they can be manually extracted without causing inflammation. Blackheads are sometimes the root of the clogged pore itself which needs to be extracted for the pore to be completely cleaned out. Whiteheads should not be messed with unless they start to get inflamed which makes it easier to extract the root.
I believe the knees are more of an uncommon place to get clogged pores because your oil grands aren't as strong there so that is odd.

Overall id say your work is not helping your skin but it is not the reason. I would ask a dermatologist about it, because if it persists you should get prescribed something. Dont wash your face/body to much even though you feel the need to in your dirty workplace. Over washing I hear can actually cause clogged pores to develop because you take away the face natural oil.