I think the way he touched his lips don't necessarily means he knew it was Katherine and not Elena. Probably when he touched his lips he was wondering why she did that, oder was bewildered, idk. It's just my opinion.
I thought exactly the same thing, but then I remembered something from the books. If Du read them Du know they're different from the show, but when Katherine showed up on the Bücher it was because she wanted them to know she was there, but before that they couldn't sense her. It happened because she's older and stronger than both of them, so even though they (especially Damon, since he's stronger)looked for something that might have been causing some bad things that were going on the town, they couldn't find her. She was hiding her presence from them, so I THINK that's probably what she did on the Zeigen too. I hope it helped! =)
i think it was because he was distracted, he's crazy about elena, but if Du think about it,in the Bücher Katherine was a cat in tye house for a while and damon of stefan didnt know, but wat i thik is that he knew something was up..... cuz why would elena KISS him?... anyways so yeah thas my theory. hope it helps.
well. i can't remember if on the series is like this, but i'm pretty sure on the Bücher they can sense the power that comes from others vampires, unless the other is so much stronger that he/she can shield themselves with it so no vampire will sense them without he/she wanting to, and that's what Katherine did on the books.
if damon can sence other Vampire and he did not know it was katherine it could be because katherine was "masking her powers" like she did in the books.(in the Bücher she was the one that lead stefan and damon to fell's church(mistic falls) and they never knew that she was doing it)
Vampire can't sense other vampires, but they can 'sense' humans especially when they KISS (like Stefan,Anna etc). But Damon was kinda of distracted ,vulnerable and surprised that Elena wanted to saved him, about the fact that he kinda feels human again etc, so he didn't notice that she wasn't Elena right away. I think he did realized that after they kissed when he touched his lips..