knocked off just before.

[flytothesky]

Hello~ Can you help me say this naturally please?

Boss: Let Mr. Lee come to my room.

Secretary: Sorry but Mr. Lee knocked off just before.

Boss: Oh, then ring him, if he hasn’t arrived at home tell him come back office.

[abaka]

Boss: Please have Mr. Lee come see me.

Secretary: Sorry. but Mr. Lee has just gone out. ["Has just knocked off" is inappropriate for this situtation; it's much too informal. Note the office is formal enough to use last names. But even if it were on a first-name basis, "knocked off" would still be too informal].

Boss: Oh, then ring* him, if he's not at home yet tell him to come back to the office.

*"Ring someone" is rare in N. American English. "Call him". Or, better in context: "Get him on his cell phone".

[flytothesky]

Thanks for your help

What about this situation, can I say 'knock off' ?

There are two close colleague.

A: ⓐHey, what are you going to do after knocking off?
ⓑHey, what are you going to do after leaving office?
Let's have a beer together?

B: I can't, I have to work late tonight.

[flytothesky]

Thanks for your help.

Would you check one more sectece releted to 'knock off'?

A and B are close collegue.

A: ⓐHey, what are you going to do after knocking off?
ⓑHey, what are you going to do after leaving office?
Let's have a beer together, I will buy.

B: I can't, I have to work late tonight.

[stuartnz]

Thanks for your help

What about this situation, can I say 'knock off' ?

There are two close colleague.

A: ⓐHey, what are you going to do after knocking off?
ⓑHey, what are you going to do after leaving office?
Let's have a beer together?

B: I can't, I have to work late tonight.

I'm not a professional teacher, but I would say that if the two colleagues are sufficiently familiar for one to invite the other out for a beer"what are you going to do after knocking off" would be perfectly acceptable informal English. To my ear, it sounds more natural than the second option you presented.