I am unfamiliar with the product but Wiki says:
When in contact with human blood or blood clots, it exhibits a strong fibrinolytic activity and works by inactivating plasminogen activator inhibitor 1 (PAI-1). Although it should be expected to be digested and inactivated in the human gut like other proteins, a few researchers report that nattokinase is active when taken orally.
Wiki also says:
In spite of its name, nattokinase is not a kinase enzyme (and should not be pronounced as such), but a serine protease of the subtilisin family (99.5% identical with aprE).