I started a new game when I got Hearthfire and I completed all sorts of quests and was offered land in Falkreath and Morthal. I completed the main quest in Dawnstar, completed all of its inhabitants' quests (except Silus Vesuius') but the Jarl, Skald the Elder, still won't offer me any land. He never asked me personally to kill a giant either. I couldn't get any radiant quests from the Inn until I reached level 20 and got invited to the museum and accepted that job. So now I've completed 4 radiant quests to kill giants on top of everything else and still nothing.

Is there a console command to trigger the option to buy land?

I've discovered the problem and it isn't a bug. Your character has to be at level 22 or higher before the Jarl of Dawnstar will ask a favor of you which will lead to the land and opportunity to become thane.


http://www.uesp.net/wiki/Skyrim:Kill_the_Giant_%28Jarl%29