Video below of the spot I used to get the 'Kangaroo' skills. As shown it takes a little more than 4 minutes to get them all, goes really fast. Just remember to use an Offroad vehicle, I personally used the Lamborghini LM002, fully upgraded.
Also, this challenge has appeared 3 times in the past, so if you remember
then this will just be a refresher.
For reference, 'Kangaroo' skills are getting multiple 'Air' skills in quick succession. My favorite spot was the fields East of Yarra Valley Horizon Festival, but the spot I use in the video is the hills around Redstone Gold Mine in the Outback. Getting quick jumps very easy in this area.