Tom's answer is a good way to do it, but if you're interested, to do it only in the expression, just add a couple of lines at the start like
myDuration = 5; // the duration of the animation in seconds
let completion = Math.min(time/myduration, 1)
and then in the for loop, substitute "360" with 360 * completion
for (var a = 0; a < (360 * ...
Press the triangle marked "Add" next to the Contents of your shape layer.
Add a "trim path"
Add a keyframe to the "End" parameter of 0%.
Move along your timeline.
Add another keyframe of 100%.
Your path will draw on.
You probably don't want to fill it until it is drawn.
Assuming that it's not changing perspective or moving around too much, I would use a tracker on the tattoo and a clone stamp from another area of skin. More elaborate removal could be done with Mocha, or using a mesh warping tracker like Lockdown, which has a demo of tattoo removal in their showreel at 0m24s:
Video editing (cutting) is best done with Premiere Pro and animation with After Effects. Both are complex software tools that require lots of training. You should invest more time in training or maybe choose different products, if they simply don't fit to your style of working.
Create a sequence in Premiere where you can easily have as many clips in a track ...
Apologies if I've misunderstood, but you can just click on the Add triangle, and add a fill or a stroke to your shape:
The modifiers in the "Add" menu are hierarchical - so you have to add them below the path's hierarchical level.
This YouTube tutorial explains how to do this:
After Effects Quick Tip - How to Add Auto Opacity To Layers and Footage
Add an expression to the layer's Opacity property by alt-clicking the stopwatch.
Paste this expression into the box:
fadeDuration = .5;
Math.min(linear(time,inPoint,inPoint + fadeDuration, 0, 100), linear(time,outPoint - fadeDuration,...
This is very similar to your other question:
In After Effects how can I generate the value of an opposite x position and then send that value to an effect on another layer?
The answer is the same. Use a pick whip to link two controllers together.