20 week detailed scan will be at ADC, Level 2.
28 week growth scan will be at AMC, Level 1.
It is to check on baby's growth, weight, all the necessary in baby and amniotic fluid too. If you need to reconfirm gender, you can also ask them to check which I did at ADC and AMC.
Not much tips but whatever you have did in 20 week check up prep, you can do. ADC and AMC is different clinic in KKH hence why you have this two clinics to visit on the earlier part and later.