[ScotsGirl]

One of our piglets has had the odd cough. He seems fine and it is not constant, only coughed twice today, so hoping it's just something he has eaten. Will it be obvious if something more sinister is going on. Others are fine.

[HappyHippy]

Pigs do get coughs and colds the same as us, so if he's active, happy, eating etc it's most likely nothing to worry about. If you can, check his temperature to rule out infection and take it from there.
What age is he, has he been wormed and is there plenty of ventilation in his arc?

[Marches Farmer]

Keep an eye on him in particualr if the weather changes - warm to cold or vice versa in particular, or wet and windy if you have them outdoors.  That kind of extra stress can quickly tip them over into pneumonia.

[Tiva Diva]

As HH says, pigs do get coughs and colds just like us - in which case I'd expect all the others to get it too 
Other things that can cause coughing are:
Dusty living quarters - what are his like?
Worms. Not Likely if you have a sensible worming strategy but possible.
Heart problems - but not likely if he's active and lively
Hope he's better soon!