Drawing on rounded surface

Hello there guys, I am currently stuck. I have done everything I would know uptill now. I am wanting to do the following.
Draw a line at roughly this point (BLACK LINE BELOW BLUE STRIPES) so that I get a new “square” which I could then extrude outwards to build a “hook” which could latch into things. Specifically speaking this would be a replacement part for a hoover. Problem beeing is that I cannot draw a line on a rounded surface. (Kind of a noob when it comes to this, however I am greatfull for every single answer)

Hi @Smithy! Yeah, lines can only be drawn on planar faces/surfaces. But if you create a plane somewhere around the curved shapes and draw a line on it, it can be projected to the curved surface :slight_smile: