How to use logic analyzer?
As far as locating where to connect the logic analyzer it is between you and the PCB. Without you posting schematics and board files. 

To analyze I2C there are 3 connections that need made. The data line, the clock line and ground. In the logic analyzer software you will designate where the clock and data lines are hooked up. Finally using the software record a window of data. Once the recording is complete the software will display you what was captured. The software will decode the data if any is available and display it as either hexadecimal or decimal.