To view anyone’s character profile, all you need is their battletag (just hover over their avatar and their battle tag will be shown on the left bottom of the screen or quote their post that will also show the battletag in the popup message draft window):
To see my profile:
https://us.diablo3.com/en/profile/MicroRNA-1507/career
Also, you need to know the region. If I wanted to see your profile, I would change the “us” in the web address to “eu” with your battletag.
To view anyone’s post history on the forum, simply enter @Battletag in the forum search window. For me, use: @MicroRNA-1507