Providing the AdBlue has the Number on it recommended by Jaguar you should be alright, depending on your mileage that would give you an idea how many litres to add .
They say that the usage can vary between 500 to 800 miles per litre,i think with my XF i'm travelling about 600 miles per litre and that AdBlue may only have a 2 year life span and if you don't do a lot off miles then only add 5 litres.And it is recommended not to Overfill when Topping up.
The fluid can crystalise and if that happens it will cause problems ( ie injector may need cleaned or tank may need to be drained ) and according to some owner's it can be a DIY job.
My XF had the AdBlue filled by the garage when I bought it and come October that will be 2 years ago, i've checked on the car computer and it's telling me the i have 3355 miles left and seemingly it will give a warning when to add the Fluid ,i believe that some owner's wait till the mileage comes down to about 500 miles before adding any Fluid.
To check the Service and AdBlue, Switch on the Ignition by Pressing the Stop/Start Button but Don't put your Foot on the Brake Pedal ( ie Don't Start the Engine ) and Scroll the car Computer till you come to Information and then you can check your AdBlue mileage.
I've heard that some owner's buy it from Screwfix ( Redex ) and some from Halfords, and it's been said that not to buy from a garage forecourt where it is being Stored in Brilliant Sunshine.
Regards Tom.