If you're on the non-vanilla servers, you can buy an upgrade to make it like that. Otherwise, if you're on the vanilla servers, nope (unless you throw the knife from a far distance apparently). The knife is naturally a 2 hit weapon when it comes to vanilla TTT servers.
The knife, as stated by others up above is 1 hit with the upgrade found under the TTT section of the pointshop (For around i'd like to think about 45 thousand points (without a donation rank so no discounts) or less?) accessible via f3, on Vanilla the knife can be a 1 shot if thrown the maximum distance (As a side note, I do not know this exact distance but its around the max distance it can be thrown.)
Sorry for going mildly off topic, but I have to ask. How do you get your animations of moving and such like that? I'd like to be able to see more of my screen much like that.
I think what you are speaking of actually is only present when I'm playing back a demo, not during actual gameplay