It is recommended online that you grow Puakenikeni using the air layer technique, because the mortality rate/success rate of PKK from cuttings is so low (I think the average percentage from a number of different sites online is around 90% mortality)
BUT, I did successully root 3 out of 10 cuttings I tried last year; started them right around this time, maybe about a month earlier or so actually. I rooted them as I rooted all cuttings, I didn't find out about the mortality rate and whatnot until I researched it online AFTER I tried to grow them (figures...).
I just dipped the cuttings in rooting hormone and pushed them into a peat/sand/perlite mixture, and misted these once a day until they rooted, it took about 2 months for them to show any sign of growth. Was alot of time, and like I said, I got 3 sad little plants to show for it (cuttings I tried to root were about 3" in length) which I forgot about and let dry out...Awful after all of that time put into them, but anyway...

I've recently started rooting Ti and Hibiscus in ziploc bags, makes it a bit more "set it and forget it". I fill the bottom of the ziploc with the peat/sand/perlite mixture, dip the cutting, stick it down into the soil, mist it a little bit, poke some holes in the bag with a needle so the airflow isnt completely cut off but the humidity is still trapped within to some degree. I have had NEARLY 100% success with this method growing Croton, Ti, Hibiscus, Fig, etc. but have not yet tried it with PKK. Using a similar, but a bit drier, method for Plumeria.

If you'd like to go ahead and try and airlayer, I've set these up before as well and can give ya my experience doing so, I just never saw the end result as they were for other people. Hit me up and I can give ya some tips on this method! =]
It's completely "set it and forget it", in fact...it will drive you crazy if you run out and check it every day, lol.

Take care and talk to you later, hope this helps a bit,

Dave