This is the license of the example project, the license of asm-dom is in the root dir

In the "How to apply this license" section it is not mentioned https://choosealicense.com/licenses/mit/

If someone has more information or links about that, please let me know

The only reason to put the license in every file is if the "project" is really a loose collection of independent files, or if you stay up at night fearing a madman on the loose randomly downloads and reuses single files from your projects.

MIT specifically calls out that the notice must be included in copies of "substantial portions" of the software which makes no sense if the entirety of the notice is already part of every file.

> The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.