Pogba is very much an enigma - like many young, talented players. He's at an age where he should be knocking on the door of discovering his true playing style and in truth, I think he is.
What do we know about Pogba? He's flamboyant & charismatic. Regularly portrayed, in not only his hairstyle/dress - sense, but in now he carries himself on the pitch. He's like a split personality of a football player. His mirrors attributes of many players - Vieira in how he carries the ball and similarities with the long, lanky running. Also in his power and ability to use his strength. When you move past this, he has a vision for a pass that few in the modern game can claim - his trademark being the scooped 'over the top pass' which regularly works.
Where I feel he is weakest is that of defensive positioning. This has been highlighted in many scenarios. It's for this very reason that I'd nearly abstain from positioning him further back the pitch. As has been said above, against the 'lesser teams', he's more than capable of playing as part of a midfield 2. When it comes to opposition, driven by passing and ball retention, Mourinho will almost certainly adapt to a 3 in the midfield. When this occurs, Pogba will not be tasked with the defensive aspect of the midfield 3.
In my opinion, I don't think Pogba even knows where he is best suited yet. Before we can actually pinpoint his strongest position on the field, I think he needs to understand the type of player he wants to be. I genuinely believe that he wants to mirror many players and while he's doing that, this is where the frustrating aspect of his game arises - in being, he tries to do too much and often over plays simple scenarios. Ultimately, it's up to Mourinho to establish this and assist him with development. The next 12 months are crucial.