As pointed out, your liege's opinion of you can influence their decision to press the claim on your behalf. The target of your claim also has to be achievable for your liege. If Sweden is much less powerful than Norway, you can't make your King like you enough to ever go to war.
One way to tip the scales there is weaken Norway through other means. You can assassinate high-martial rulers to decrease the amount of levies they can raise. You can assassinate popular Kings of Norway, as lower liege opinions results in lower levies that can be raised. You can use your chancellor to sow dissent.
Ultimately, if you get the opinions low enough, the holder of your claimed titles may go into revolt. If that ever happens, you can declare war on the revolt faction instead of the King. You'll be hostile to both sides of the revolt, but the AI generally will focus on the revolt instead of you. If you get to 100% warscore first, you win territory from the revolt faction and Norway does not reclaim it when the revolt ends.
AI characters often take advantage of revolts like this to press claims (provided they are at least equal to the belligerents in terms of military power), so causing a revolt may be enough to get your King to go to war for you.
If your liege does go to war for you, don't forget to raise your own levies to pitch in, essentially providing your cause with bonus troops. This is a crucial advantage over AIs, because AI vassals will never raise their own levies if their liege is the primary attacker or defender.
(The only time I've seen AI vassals and lieges both raise levies is when they both join someone else's war, usually in a Great Holy War – Crusade or Jihad – but more rarely when they're both allies of another ruler who calls them into their war. This can get quite common and hairy when you are successful at spreading your own dynasty over half of Europe.)