Through doxxing someone could essentially find out exactly who you are, and if they're able to connect your Bitcointalk account to your identity then they definitely can find out what amount of Bitcoin you own, if they're connected to your account. Alternative, just seeing your address on something could be enough to tip someone off.

Of course, you already know this, but I always say this since there's still a lot of people joining the forum and a fair amount don't know as much due to inexperience.