Can one do whole body scan to check any kind of cancer?

Resolution of scan.: It depends on which scan we are talking. In general the resolution i.e the ability of a "scan" depends on the nature of the test. For a CT scan to detect an abnormal finding the lesion has to be greater than a cm, MRI can give an abnormal signal, a PET CT may be more sensitive. Blood tests measuring DNA or circulating cancer cells may be a more sensitive but it may not reveal the location.