Can i say
How can you even express “we don’t know anything”?, for you must think that we know at least one thing, namely, “we don’t know anything”.
Can i say
How can you even express “we don’t know anything”?, for you must think that we know at least one thing, namely, “we don’t know anything”.
Using the question mark in mid-sentence is not generally acceptable. Here is one possible rewriting (I've taken some other minor liberties for style, but I hope you get the idea):
How can one even express “we don’t know anything”, when one must think that we know at least one thing, namely, “we don’t know anything”?