You may use SceneJS under the terms of either the MIT License or the GNU General Public License (GPL) Version 2.
The MIT License is suitable for most projects because it's simple and unrestrictive, however if the GPL suits your project better then you are also free to use SceneJS under that license.
You don't have to do anything special to choose one license or the other and you don't have to notify anyone which license you are using.
You may use SceneJS in commercial projects as long as the copyright header is left intact.