What is the best way to get rid of 3 corner jack prickles from my yard

Yikes, these sound deadly! See if this will help you.

https://questions.gardeningknowhow.com/3-corner-jacks/

Never heard of it before. I learn something new every day. :-)

Boiling water kills just about anything!

Hi Don, hope this helps you.

Three-corner jack can be controlled by spraying with commonly-used nonselective herbicides and some that allow grasses to survive. Only a small proportion of the seed bank of three-corner jack germinates in each growing season.

I heard it recommended to put on very thick thongs and walk back and forth over those removing the thorns. Take the shoes off and rub them togather to get the thorns out. This was on Reddit.

Cut them back and Dig them up!