When I use Google Talk over
https://gmail.com can anyone read (sniff) my messages?
If you are on a channel where it is easy to sniff the sent data, i.e. on a switched LAN or on an unsecured WiFi network, an attacker could only see the encrypted data and not the plain text you are sending.
Take a look at the security information your browser shows you:
Here are the relevant bits:
Not generally, but it doesn't mean that someone is not viewing or storing the conversation. Since the connection is encrypted, it will not be captured in transit, but if you are using a company computer, and they are using a monitoring application like Spector 360 from SpectorSoft, either on your end or the other, than that conversation can be recorded and stored.