You probably want to use two way binding between component scopes.
parent-container scope should have selected attribute:
can.Component({
tag: parent-container
template: '
'<notes-list selected="selected"></notes-list>' +
'<note-editor selected="selected"></note-editor>',
scope: {
selected: 1 // some initial value (for example ID) of selected note
}
})
After init both notes-list and note-editor will have selected attribute equal to 1.
And as attributes two-way bound you change selected value say in notes-list it will be updated in parent-container and sequentially in note-editor.