What is the goal of this plugin? (It rather sounds like a clone SketchUp. Do you have an idea what effort that requires?)
How is it related to MySQL?
How is it related to the CityEngine link?
Before planning an extension or even a software, you need to know the goal and what technical prerequisites you need to realize it.
You are aware that .skp is a proprietary undocumented file format. You cannot trivially open it in a self-made viewer.
There exists a binary SDK for reading .skp files into an external software (no SketchUp needed). This SDK is only available for MacOS and Windows.
You can also make a SketchUp extension to export the .skp model (from running SketchUp) into your own file format, which your web viewer can read.
You can make an extension that reads in SketchUp all component attributes and sends them to a server e.g. as JSON.
There exist already several universal attribute editors. Basically you could take one and restrict it to show only your own attributes.
There exists also an extension to export model and attributes to CityGML which CityEngine can import.
Main goal is connect Sketchup file with MySQL and web 3D viewer
I need to storage Component Atributes in MySQL to show and edit them in the web on site. And then I can see it in the Sketchup file. If it’s possible of course.
Nope, I link CityEngine viewer as an example of Web Viewer with layers control. Just this.