At this point, we're only defining “truth” and stating that it’s possible to know at least some things are true.
If you say, “I know truth can’t be known,” your statement contradicts itself. You are implying that you DO know at least one truth, that is, “truth can’t be known.” Furthermore, when you state, “truth can’t be known,” we know a truth about YOU. We know that you exist. We’ve proven that we both know at least one truth!
These are just a few examples of things we can know. There are more examples too; it can be proven that 5+5=10 and that Alaska is the largest state. We know that some facts are true.