We try to avoid spoilers in titles already, per site policy. However, what's considered a spoiler varies person to person. We run into the issue of people not wanting spoilers blocking the tag for awhile, so only people OK with or lenient towards spoilers see questions to edit them.
We don't have control over what's HNQ outside of what the masses happen to vote or answer on to trigger the HNQ algorithm. We really can't help that. Ignoring tags on our stack, such as game-of-thrones, won't hide it from HNQ, either.
The best advice I can give you is to just assume they're about older events. We get plenty of questions about previous seasons. That, or just don't let it get to you (there's some research that spoilers can increase your enjoyment, actually!)
I don't watch GoT, but I do know a surprising amount about the show just from news headlines and posts. The number of times Jon Snow has filled my news feed is frustrating (I don't even know what he looks like). I feel like HNQ may be the least of your worries!
I have had the Internet spoil some key The Walking Dead and Doctor Who moments for me, so I understand it happens. I've just started rolling with it and focusing more on the parts that headlines don't talk about.
I wish there were more we could do, but I do think we do about all we can.
Perhaps if we're lucky, someone can make a browser extension to hide HNQ questions based on Stack...