When I engage VCALC, there is a alert message to inform me on GTN display.

Is there option to engage sound alert too?

Hi,

can you please detail what alert is this? Is there a sound alert supposed to be audible too? You might want to cross check this in the Garmin GTN Pilot's Guide.

VCALC calculate T/D (top of descent)  on the route and show remain time to t/d (hh:mm:ss). When reach T/D, there is a "message alert" on GTN screen. There was not (sound) audio alert.

I asked is there option to enable sound (audio) alert (example as horn).

Also one more question, Is possible to show t/d on map?

I'm not sure the real GTN is supposed to make an audible audio alert for this. You might really want to review the Garmin GTN Pilot's Guide for all the configuration options, features and expected symbology/alerts.