might be looking at a 06 low mileage diesel ,what should I look out for or what should have been done on the service at this age.? even with low mileage.

have a look in the general section tolley, there's numerous threads re 'what to look for' in there, there's also an excellent buying guide in the wiki...

It would benefit you if you posted what your budget is as there lots of cars out there that other members have seen.
 2020 Porsche Panamera Turbo Hybrid (V FAST)
2017 Range Rover Autobiography 5.0 V8
2018 JCW Mini Cooper
2018 Skoda VRS

'06/56 is right on the cusp of TD6 and TDV8, so your budget will dictate which one you look for

Edited to say - Sorry, misread your message, I expect on 06 will be a TD6  Got - 2017 SDV8 Autobiography in Loire Blue
Had- 2008 TDV8 Vogue SE in Java black
Had - 2007 S/C in Stornoway Grey

only say 06 for the lower tax, would love a HSE, been offered one with just under 50tho for £13000