For chilled water system I would like to know to best way to connect the automatic chemical dosing .and where we have to to take the ph reading from supply or return line.and where we should fix the dosing point in supply or return line I wish to get answer for this question with convincable reasons.. thank you a lot

You need not required,
1. just see supplier recommendation
2. or use soft water with recommended chemicals, u can also call other water solution suppliers for selecting the required chemicals.
3. check water quality in every six months (CaCO3, pH, TSS)