Why would you have a problem with this? You would use the present perfect to express something that happened previously, without specifying the time. 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.
Recently one of my friends told me that there is distinct difference between 'know of something' and 'know about something' expressions. Please let me know as soon as you figure it out. I saw this sentence in the book 1q84:
Alright, well, for example, like on saturdays, y’know, what i liked to do. It's not just you that don't know. I already know how to turn on the television. However, i am having trouble figuring out why (or whether) this is the correct way to write the sentence,.
In (2), however, the object of. Also explain the difference between the two, thanks. '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 know (about) this difficulty/problem. I know how to drive a car.