You would use the present perfect to express something that happened previously, without specifying the time. 'know of' is used when you have personal. In the first sentence, it seems to me that to know expresses that the speaker experienced the problem/difficulty.
I already know how to turn on the television. Also explain the difference between the two, thanks. I saw this sentence in the book 1q84:
Recently one of my friends told me that there is distinct difference between 'know of something' and 'know about something' expressions. What is the correct usage of phrase you don't know what you don't know? However, i am having trouble figuring out why (or whether) this is the correct way to write the sentence,. Can it be used in formal conversation/writing?
I know how to drive a car. It's not just you that don't know. I know (about) this difficulty/problem. Possibly, i do know that can in fact only be used, when, you are answering the question of whether or not you know the issue at hand (or your knowledge has been called in.
Please let me know as soon as you figure it out. In (2), however, the object of.