There is a feature in this game, been here since February of last year, that can and will be able to just about instantly help you find out where it is.
On the Map it's called 'Show Active Quests', and like the name implies, it is great with just about every quest helping you know where to be.

If the name of the Quest that you are looking for is colored Red then you have to move to each of the 8 other mini-Maps and then look using that feature again and again...
At some point it will be colored Green and the one and only particular square that the Giant is in will highlight and center on your screen.

If its Red everywhere then you have to look at the few unmapped areas in the game where things can spawn.

I am assuming that both of you actually have the Giants quest in process.
This method should find it just about instantly in any of the 150+ squares of the 9 Maps.

If on the other hand your Quest is not in process, i.e. it is in the Completed Quest Log (even if it says it is repeatable) or is in neither quest log (because of the fact that inactive not in process quests older than 5 days disappear to declutter the log). Then no amount of looking will find it because it does not yet exist. But actually that's a little false. If your quest is poised to be available you CAN make it happen in either of 2 squares JUST by walking back and forth hundreds of times between both squares.

There are only 9 maps.
One only needs to move into at most 9 of the maps. And luck should make it perhaps half that.
And once there hover your mouse over the name of that quest when one has 'show active quests' activated.
And if the name is Red on all 9 of those maps then one must look at all less than a dozen non-mapped squares individually by going to each and every one of them and only them. And those really only have to be places you have been to recently whenever it was when you lost these quests. i.e. I have not been into The Frozen Storehouse in many months so I'd never have to check for anything there.

But because there is a fault with what should have been a great addition/improvement to this game on Friday the 13'th (and still broken) there is one other thing you can do to help find them.
With or without 'show active quests' On you can hover your mouse over any of the squares on each of the maps that can, but might not currently, have ? or ! on them. That is the quest could be hiding on any of the squares that can be the start or end of a quest. But unless you never do quests again and again you should have seen them each and every day since you lost them. And when I say 'squares that can have quests' I also mean the 8 transition squares to the 8 other maps, and the transition square back to the main map. Some one of those squares should have a 'quests ending here' that includes fe-fi-fo-fum and share the wealth, well whichever one is complete, the other one should be found even easier with the year old feature that has never not worked for me.

But Rosemary if you truly have not found them in a week of looking then if I were you I'd send a trouble ticket to the Developers and have them help you find them, and be embarrassed when you see where they were that you should have been able to find using all these instructions.