'There is no such thing as knowledge which cannot be carried into practice, for such knowledge is really no knowledge at all.' Which fallacy is committed in the above statement?

The statement begs the question.

It concludes that unpractisable knowledge is not knowledge at all.

Its supporting reason simply restates that same claim in other words.

The premise thus already assumes the very point it is meant to prove.

Arguing in this circle, where premise and conclusion coincide, is begging the question.