How to replace a spoke on a rim with no spoke holes?
It looks like a pretty standard threaded nipple with aluminum spokes. Is the spoke broken off right at/in the nipple, by the rim, or is there enough of the broken spoke sticking out of the nipple that you can 'grap' it with a pliers/vice-grip type tool? ...

a). If the spoke broke off right at the nipple, leaving nothing to grasp -- or if the nipple itself is somehow damaged -- then you'll need to remove the rim strip/rim tape from the inside of the rim in order to remove the nipple. Spoke nipples aren't threaded into the rim so it should 'back out'/fall out freely. In this case, you will need a spoke wrench to install the new spoke and you will need to install new rim tape after the new spoke and nipple are installed. You may need an sharp knife to carefully cut/lift the old rim tape.  Otherwise...

b). If you can grab the broken spoke securely, just use a spoke wrench to turn the nipple and un-thread the broken spoke. You shouldn't need to access the nipple from the 'inside' of the rim. In this case, you will need a spoke wrench (to turn the nipple) and a pliers (to grasp onto the broken spoke).