Roleplaying encounters have always been a troubled fit for skill challenges. Many of the things that make skill challenges work to handle other game situations don't work very well in a roleplaying encounter. For one thing, it becomes very difficult to put the PCs into a position where they must take turns and give each PC a chance to act. But, more importantly, the game structures that make skill challenges interesting in other situations become a distraction in a role playing encounter -- players become much more focused on the game than they are on the scene and the story playing out before them. 

At the same time, it can be helpful for DMs to have some structure in mind as they prepare a RP scene.  DMs who don't feel comfortable ad-libbing a scene may struggle without a framework to work through -- successes and failures, skill checks, and so on. Others may just wing it, roleplaying the scene and asking for a skill check now and then.

In most cases, though, a scene of dialog and interaction between PCs and NPCs will rarely be improved by being placed in the sort of obvious structure we use for other sorts of skill challenges. 

(an exception to this will be Intrigue challenges, but you're going to have to wait for the details on those….)

So, lets talk about a variation on a skill challenge -- a Role Playing Challenge.  

Important Aspects of a Role Playing Challenge

1. Interaction is focused on the dialog and interaction between the PCs and the NPCs -- not on the structure of the challenge, etc.
2. The DM may ask for specific skill checks from time to time to decide how successful the PCs are in their efforts

Preparing a Role Playing Challenge

As you prepare to run an RP scene, make some notes for yourself -- a few minutes spent thinking and preparing can give you all the tools you need to be able to focus on the roleplaying.

1. Goals, information, and limitations of the NPC -- if you know what information the NPC has, what the NPC wants out of the scene, and other key story details, you've got the most important details. 
2. Consider what outcomes you want and need the PCs to earn in the encounter. In many cases, RP encounters are really moments of exposition -- you're giving the PCs information they need to take the next step in the adventure, and without that information the adventure is stalled.  Are there pieces of information that the PCs may not need, but that could be useful, or other ways this social interaction might mitigate a future encounter? Those are the things that should be the real focus of skill checks and your roleplaying challenge. 
3. A few DCs.  To begin with, make sure you know what the NPC's insight bonus is (and passive insight score). That will give you a base DC for PC interaction. In some cases, you may want to use some other values:
   - A leader's passive intimidate or diplomacy score : A guard may be easy to convince that the PCs are simple merchants, but if the guard is terrified of his master's wrath, he's still not going to let the PCs in the city gate. 
   - Use the NPC's level to get easy/medium/hard DCs so you have some fallback DCs, just in case you need them. 

You'll find, as you work through the first few of these, that the effort to prepare a Role Playing Challenge becomes easier to do quickly, or on the fly -- but remember, what matters is the story, the scene, the interaction.