There are so many twisted pair cables around, which are claiming to be a certain class/category, e.g. CAT6. How can verify the CAT type number? Cutting them is maybe not the most practical solution.
The cable category should be printed on the cable sheath.
Just having cable rated at a particular category doesn't mean the cable plant is actually rated at that category. All the components of the cable system must be rated for that category. Also, installation is very important. Even experienced installers have problems with Category-6 cabling.
The only way to tell if a particular installation meets a category is to test the cables with an expensive tester that performs all the tests in the test suite for a category. When a cable plant is installed, the installers should test each cable, fix any problems, and provide a complete report to you.