How do I measure off coil temp and on coil temp in the split unit air con?

Are you looking to find the spilt temps? I am not sure what you want.

My question is " I want to measure off coil temp and on coil temperature for air con. The air con is split type.

If you use a thermometer that you can insert into the duct work you can check the temp of the air just above the evaporator coil, then use the thermometer in the return aid duct just below your air handler ( if that is what you are trying to do). The difference in these two temps should be 18 to 20 degrees. To lower the difference slow down the air movement across the coil, just the opposite to increase the temp.

I hope this is what you wanted to know, it is hard to determine what you are asking for.