How do you know that you know?

How do you know that you know?
Everything that one knows one has experienced through the senses, now what if all the senses are being mislead by some greater force. Now how can we know that this is real something else is not, well we can not know because we can not trust our senses to provide information that is correct or can be checked against other sources of information. We like to believe that the world around us is real, since that makes it simpler to interact with that world, yet is it real? In theory we, our minds could be in a jar, in which we experience everything, and can not even percieve reality. Since we are fed with this information from this other source. To come back to the original question, if we can not verify what we percieve to be real then we can not verify anything we believe to be true. Then logically we can not know anything, yet we often say that we know.
How can that be if we can not actually verify this 'knowledge'?