Yes you can freeze green onions and the green onions will last for up to 10 months to a 12 months in the freezer.
When freezing green onions it's best to chop the green onions up first and then place the chopped up green onions in a Ziploc bag or other freezer safe bag.
Then place them in the freezer and they will be okay in the freezer for around 12 months.
Eat the green onions within 12 months for the best freshness and tastes although they are usually safe to eat after 12 months as long as they have remained frozen.
I like to chop up green onions and freeze them in Ziploc bags and then use them in soups and stews and I just toss the frozen chopped up green onions in my pot of stew, chili, slow cooker etc.