Google Talk, also known as Gtalk, was an instant messaging service developed by Google that allowed users to communicate with each other via text, voice, and video calls. It was a popular messaging platform back in the day, but Google discontinued the service in 2017. Therefore, it is no longer possible to use Gtalk to check if someone is online.
However, there are many other instant messaging platforms available today that offer similar features to Gtalk, such as WhatsApp, Telegram, and Facebook Messenger. These platforms allow users to send text messages, make voice and video calls, and share files. Many of these platforms also have features that allow users to see when their contacts are online.