You haven’t shown it. You just asserted it.

Do you think it is possible to know whether the claim that there are unknowable truths is true?

“All truths are knowable” cannot be unknowably true.

Therefore one of these is true:

1. “All truths are knowable” is knowably true
2. “All truths are knowable” is false

The anti-realist believes (1) and the realist believes (2).

You haven’t justified (2), only asserted it.

So pragmatically that leaves us with (4) and (5). How do we decide between them without knowing any unknown truths? — Michael

1. “All truths are knowable” is knowably true
2. “All truths are knowable” is false — Michael

Answer the question I posed:

Do you think it is possible to know whether the claim that there are unknowable truths is true? — Janus

It is obviously impossible even in principle. because no matter how many truths we know there could always be an unknowable truth.

But then if the truth as to whether there are unknowable truths is known to be unknowable, then we know that there is at least one unknowable truth. Address that and stop with the red herrings.