On most cables, you should be able to look at the cable itself and find the label printed on the outside surface of the cable. That's your best bet. Cat-6, 6a, and 7 cables are generally thicker than Cat-5e cables, and less flexible—so if you're used to handling Cat-5e cables, that's another easy way to tell.
Most people don't really care whether they're using Cat-5e, 6, 6a, or 7 cables at home. The Internet connection is the bottleneck, faster cables won't help that. Using a Cat-6, 6a, or even cat7 cable can enable faster speeds when transferring files or otherwise communicating between two computers on the local network, but the truth is most people won't even notice.