Using a Coated Knife to Strike a Firesteel
A firesteel requires a striker, of course. While it's possible to use the sharpened edge of your knife to get sparks flying, that tends to create a "dull spot" you'll have to touch up later.
A better solution is to strike the firesteel with the spine of the knife -- but if your knife has a coated blade. you'll have to remove a small amount of the coating.
Using a small file (like a triangular needle file), carefully remove the coating from a section of the knife's spine (circled in the photo). Try to maintain the squared profile of the spine, remembering that the idea here is to create a bare-metal section with an edge that'll get a good "bite" into the firesteel.
That's it -- now you can use the spine of your hard-working knife to strike a firesteel!