example dialog:
"yes, yes, it's your job. I know that."
Can I just say "I know" instead of "I know that"?
another one: do I say
It is very pretty. Where did you buy?
-or-
where did you buy it?
example dialog:
"yes, yes, it's your job. I know that."
Can I just say "I know" instead of "I know that"?
another one: do I say
It is very pretty. Where did you buy?
-or-
where did you buy it?
(1) You can say "I know" or "I know that.
(2) You really need the "it' here. "Where did you buy?" sounds incomplete, leading to another question, "Where did I buy what?"
I think the difference may be that in sentence 2, you're referring to a thing, so the "it" is standing in for whatever was bought, while in question 1 "it's your job" is an abstraction, so somehow it's OK to just say, "I know."
In dialog, you would usually say "I know that" as a simple statement. "I know" would be accompanied either by a gesture such as holding up your hand with the palm toward the other person to signify that he doesn't need to say any more, or by significant stress on the words to send the same message.
This may not apply outside the US.