Hi,

I got Sonic Lapis LVL2 as reward. What is it and how do I use it?
What is the best chance to like it?

Thanks

You can link a sonic lapis on your boots, it gives +2 in move speed (you'll be in "very fast"). You have around 20% to link it with an Operator hammer if I'm not wrong.

20% is correct, though it will be higher at a guild warehouse, and higher still if there is a bonus linking chance on.
I would strongly recommend waiting for a 10% bonus linking day as you will get a 32% chance for linking.

Be warned though.
A sonic lapis will break your gear if it fails to link.
Make sure you have a lucky charm to prevent this happening.