4.3 Lockscreen: How to drag on a lockscreen notification to go to that app?
The answer is indeed as Dan Hulme mentioned:


Tap once on the notification (SMS, phone etc). This makes that notification shrink and fade, when in fact it's selecting it; extremely unintuitive but that's the way they implemented it...
This makes an empty grey box appear in the bottom half of the screen with no label. What you need to do now is drag across this box. Again, no label, no instructions, no suggestion, bad UI; but it does what you want: unlock the screen and go to the app corresponding to the notification (SMS, phone, etc).


Thanks Dan for the answer.