The iPad Air2 I want to buy has a model number MGKL2B/A but I was told to look for A1567. Which is right

The iPad's model number (the A.... number) is on the back of the iPad, and A1567 is the iPad Air 2 wifi and cellular model (A1566 would be the wifi-only model) : Identify your iPad model - Apple Support

The MGK number (which shows in Settings > General > About > Model) is the model/order number (and the number that you've given appear to be a 64 gig wifi-only iPad) - those numbers distinguish iPads between different countries and their capacities, so there can be multiple M...../. numbers per A.... number

Googling shows that MGKL2B/A is an

Apple iPad Air 2 64GB Space Grey Wifi

that was made for the UK market