Where do people have their jack lines placed? Attachment points?
We have not placed them yet/before so would be curious.
Anyone have suggestions?
I guess the answer is that no one uses them!?!?! 
We always use ours for any long passage or if we are going to sail overnight. They are part of our “going-to-sea” check list.
We rig them from the cleats on the cross-beam to the rear cleats looping them through and over the cleat - it’s tight to get them on - but secure. That covers a run along the side deck to the tramps.
I have also fabricated some dyneema runs to the mast - a locked eye-splice at each end - one end goes around the mast and out to the jack line which then runs through the loop on the end. That allows us to stay clipped on all the way to the mast if necessary.
When I have to go forward, I don’t want to get into the position of wishing I had fitted the jack lines - it’s too late then…
To be honest I am surprised that the delivery skippers don’t rig the lines for the delivery trips. Our jacklines were fitted in Knysna before we left for Cape Town and have been fitted for every passage since.
On handover from Knysna the zig-zag stitching on the loops was - in my opinion - not strong enough for a safety device. So mine went back to be properly stitched check yours and make sure you are comfortable that the stitching is strong enough to tow your whole body through the water at sailing speed… (look for stitching similar to the harness line)
We always bring the jack lines in after passage, wash them to get rid of the salt and store them away so they (and the stitching) do not get UV damaged.
I’m pleased to say we rarely have to clip on to them and they have never been put to the ultimate test - long may that continue…
The black tape in the photos is the Jack line.
We ran them from the aft cleats to the cleats on the front cross bar. Then another across the bow just in front of the mast. We ran another across the stern just behind the walkway in front of the dinghy.