TRRS

Adding the TRRS before the switches is best as you can then test both board halves before covering up the diodes with the switches. The TRRS jack body goes inside the white outline. The TRRS jack goes on the front, but is soldered from the back. Taping it down temporarily is helpful.

Then solder from the back. Where you solder will be mostly outside the outline on the back, as the outline on the back is for the TRRS jack body for the other half of the keyboard.

Take care to not create a solder bridge between the rear pin and the hole next to it.

Next: Handedness Jumper