I did this on my Legendary run, without reading any guides and it wasn't hard at all.
In the very first core globe you come across on this level, while you're still on foot (therefore before the Mantis part), after clearing the area from enemies with the help of your team, if you look to the sides there will be "walls" where you can climb up to.
Choose one of them, preferably one where you can face the core straight ahead. Watch the rings rotation and observe its revolution pattern around the globe, so you won't waste time with unsuccessful attempts to hit the core.
You want to jump and hold in the air a little before the core gets exposed (all rings aligned to the side), using the stick to adjust the aim on it and then ground pound it.
As I've said before, just be patient and pay attention to the protective rings pattern so they won't block you from reaching and hitting the core.
If this solution helps you in any way, feel free to leave it a thumbs up. Thanks.