The process used to determine what the artist was trying to convey.

The answer is Interpretation
When creating an artwork, artists often put his emotion, principles, or pollitical value into his artwork and does not give any information about it for the audience. When the audiences see the artwork, they would combined the artform that they see with their own emotion/principles which lead to the personal interpretation on what the artists actually want to convey.

The process used to determine what the artist was trying to convey is the practice of art. Whether that be through sketches, music, speeches, painting, or writing. When something is in it's art form, it's simply the best.