Mike, K7MH provided you a very good link for your computer control issue, HOWEVER note that you may have 2 issues to deal with.
Are you really asking Where is J22 - in this Icom 735 radio?
J22 is on the PL board inside the Icom IC-735 UNDER the Power Amplifier (PA) unit.
To gain access you need to remove the top cover and the 4 screws attaching the PA
You can set aside the PA unit by disconnecting the power cable to the PA unit.
CORRECT reassembly -- PATIENCE REQUIRED (not shorting or pinching cables) is required to have a FUNCTIONAL Radio (and avoid damage).
When GI0ZGB removed his Icom IC-735 case covers to change the baud rate from 1200 to 9600
he had to remove the substantial heatsink to access J22 - THAT may be a bit much for a borrowed radio and your experience.
1. You original question 1200 -> 9600 baud
# IC-735 using address 04 hex and 9600 bps.
The second issue is the Icom CI-V network (which is also addressed on that same web page)
2. Proper settings for the Icom CI-V network
# Almost every rig requires an ICOM CT-17 CI-V interface or compatible. A great list of CI-V interfaces can be found at the website from Ekki Plicht, DF4OR.