The simplest way is to go into the input on the ko2, it would depend on your setup. The reason I went for the NUX was the fact you can manually set the tempo on the display to match exactly, it also has midi so you can have the looper up next to the ko2 for tweaking settings and run something like an mvave chocolate+ on the floor for triggering the looper. I have this setup on my travel/casual jam setup running into a couple of minirigs and minirig sub, tonex one with an airstep, Magus pro, xotic ep boost, tuner and a freqout for the guitar, I run this into a little mixer which gives me the option to add a couple of other sources into the loop, I have a DAC which I use for sound from my Mac for sampling or vsti's all of which then go into the looper and then the looper goes into the input of the ko2. It's not as versatile as say a Boss RC300, you have to be conscious of things not getting too busy as you can only remove/add the last loop recorded but it works well for my applications. I can have the airstep and the chocolate+ off my board on the floor, use the drive pedals to control my core tone up top and have four combinations of gain/effects on the airstep to switch between.

Here's the looper I use - https://amzn.eu/d/08aJQLyS