My recirculating line underneath my slab had a pinhole leak and so I had some plumbers seal it off. The plumbers warned me that I will likely get more pinholes and having a recirc line underneath a slab is not great because repairs require sledgehammering into the floor to fix.

Now I don;t have great hot water around the house. I am guessing I need to build a new recirculating line. My house is unfortunately not configured all that well to do this through the walls or the ceiling.

Is it common to build a new recirc line on the outside of the house? Also, is it required that I connect it to the furthest pipe?

Thanks

not common around here because of freezing temperatures but it that is not a concern then it will work.
tie the recirc between the last and next to last fixtures.

It doesn't HAVE to be at the furthest pipe, but you will only have "fast" hot water up to the point where you do connect it.

Do yourself a favor and re-pipe in the attic if possible. Pin holes are rampant in under slab copper installs. You should shut off everything inside the home and go to your water meter to see if the small needle is rotating. If it is you still have a leak somewhere in your system. Hundreds of thousands of homes have copper under the slab and Plumbers are staying busy moving these systems into the attic if there is one. All hot water piping should be insulated if possible to conserve energy and save money. The way folks waste water is slowly coming to a halt due to limited resources of potable water and the cost to convey it to customers.