Both direct so that the battery can be charged too after disconnecting the ground.
Sorry I’m a bit lost.
You disconnect the ground whilst charging ?
So the negative charger cable is connected to the negative terminal on the battery not the cars negative battery clamp ?
I don’t disconnect it, but with the ctek connector connected this way I can still charge the small battery regardless of whether the ground wire is on or off.
And you dont disconnect the main 12v either when charging the smaller 12v ?
So just for me not to blow the car up 
Connect the quick connectors straight to the cars battery clamps on the small 12v battery, no need to disconnect any of the cars terminal clamps from the battery.
Leave the quick connector cable connected permanently to the cars 12v small battery live & negative clamps ?
Another quick question.
If both the 12v batteries do receive a charge either from the ICE or traction battery, why is there a need to charge them manually, especially the smaller one ?
Well, I’m not disconnecting it and the car hasn’t burned down yet 
The large battery charges while driving and while charging the traction battery. The small battery charges only while driving, so the less you drive, the weaker it becomes. Therefore, the small battery needs to be maintained.
Each 12V battery has a separate positive line, so charging the small battery does not affect the charging of the large battery, and vice versa.