Shaikh, the website in which I am doing online course has course materials that are freely available so I can learn whatever I want. but test or exam is not free means learner have to pay. as I am doing course only toacquire knowledge not to achieve certificate I choose to skip test. is it cheating & sin or not?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

As long as skipping the test is allowed by the site, then there is nothing wrong with benefitting from these course materials, and this is not considered as forbidden cheating or deception.

Allah knows best.