1 most accurately represents, "Learn", as it puts the user at the center of the metaphor.

2 is too generic / doesn't have clear meaning.

3 represents "code" well, but I don't see a clear representation of "Learn", and I think overall it's too detailed for an icon.

4 would be my second choice for "Learn", but I think the book opens it up to too many interpretations, and does not at all imply a video.