To some degree he has, mostly, figured "it" out.
Matt Farrell looks at him stunned and says, "Aren't you scared?"
McClane tells him(calmly), "Yeah, I was scarred"
Farrell, "This is you being scarred!"
There is also the exchange of:
Farrell "You've done this before....haven't you? Killed people I mean."
McClane "Yeah...I have"
There is also that exchange where Farrell asks why don't they just sit this out from here. John lets him know that only they know what to do and can't communicate. So they are going to do it. If he could let someone else handle it would, but he can't. It's part of the whole "And that's what makes you that guy" line in the film.
Some paraphrasing but the gist is by LForDH
and after 3 of these type situations he is able to manage it better--to a shocking degree of someone else for the first time like Matt Farrell. The series is giving the audience someone new to experience the "unexpected situation" with like we did John in the first and second Die Hard
s. Meanwhile we still get John in all his attitudinal glory while having to be in this situation...again. In Vengeance
it's Zeus(SLJ) in LFoDH
it's Farrell. Not sure that this installment will have one based on the trailer.
That said there is the elevator clip for this film where both McClane's and a third guy are in an elevator. The third guy seems very shaken but both McClane's have a firm grip on their guns. He looks at John and says, "You've done this before, right?" And John just gives him that firm assuring look.