, run the global command Preferences: Configure Language Specific Settings (command id: workbench.action.configureLanguageBasedSettings) from the Command Palette (Ctrl+Shift+P) which opens the language picker. Select the language you want, which then opens your user settings.json with the language entry where you can add applicable settings.
"emmet.preferences":{
"filter.commentAfter": "<!-- /[#ID][.CLASS] -->",
},
"emmet.syntaxProfiles": {
// Enable XHTML dialect for HTML syntax
// “html”: “xhtml”
"html" : {
"filters" :"html, c"
}
},