Invoke dialog and fill its content dynamically in CKEditor

I'm new to CKEditor development. I have written a plugin to insert custom tag element ( pre ) and update its attributes.

I want to open the plugin dialog( dialog name is snippet ) once user clicks the pre tag element, And i want to fill the textarea with clicked element innerHTML in dialog.

I have two questions.

1. How to invoke the plugin dialog dynamically?

2. How to access the elements inside the dialog?