((So I did a little research to understand this a little better. As I understand it, but you're the DM so it's ultimately your call, the actual infusion is to
replicate a magic item. In this case, I would replicate the spellwrought tattoo needle after a long rest. And from what I see, and up to DM discretion, its a needle that houses ANY spell/cantrip (I chose cantrip) as a one time use. Similar to a scroll.
So I would use the needle, it gives me a tattoo in whatever shape I want and I can cast the spell any time as essentially a free spell slot. Again, I chose cantrip so that part would be irrelevant. It also eliminates any material needs, but still needs verbal or somatic as required. Once used the tattoo disappears. But after a long rest, i can create a new needle and do it again.
Lastly, this isn't something I actually LEARN, so it's not going to show up as a cantrip on my character, but follows the rules of the specific table. In cantrip case: +3 spell modifier, 13 saving DC and +5 attack bonus.
So I guess from you, I'd need to know what restriction, if any, you want me to put on the cantrip I choose. I leave all the decisions to you because you're the DM here
))