How do investigations work?

[RemnantHelmet]

I've killed Nergigante at least 20 times trying to get the full set, and all I'm missing is the gem. I've looked online to find people recommending doing investigations instead of the optional quest, but when I go to post a quest, the investigation tab is grayed out.

Some other info:

When I go to the investigations tab while speaking to the chief ecologist, it says that an investigation for nergigante has been issued.

Just about every time I've done the Eater of Elders quest, I'll pick up some nergigante footprints or horns and see an "Investigation added" message appear on the right.

After I finished tracking and identifying the three elder dragons(after you kill nergigante in the main quest) I got another message saying that specifically a nergigante investigation has been added.

Despite all of this, the investigations tab on my quest poster is still grayed out and cannot be selected.

EXTRA QUESTION:

I've also seen people recommend going to something called the Melder. What is this? Where is it located? Apparently I need something called a Wyvern ticket and I'm supposed to complete all the weekly stuff for the research team? What weekly stuff? Where do I find these research quests or whatever they are?

Sorry if some of these are oblivious, but I've been away from the game for quite a long time and I just came back a few days ago.

[Broscar]

Go to the bounty people.
Pick investigations and select the quest you'd like to have appear in your list.

[Markzerow]

There are also limited bounties in another tab with these people Broscar said above in which you can see what tickets they are giving, if you manage to complete them. There are a bunch of tickets used there (in another tab) that come from event quests as well.

About the melder, she's the lady that helps you turn some items gained from quests into decorations or other itens. Some parts of her work are also a step later in the game, mostly when you're into Tempered monsters.

[Suzaku]

Special investigations are just story-based stuff. They don't really matter for what you're looking for.

Investigations are unlocked randomly when you pick up tracks and break monster parts. The investigation you're given is based on the locale. The monster(s) of the investigation is randomized within that locale, so you might pick up tracks in the forest from Tobi, but the investigation it spawns could be to fight a Rathalos in the forest.

The Melder can make certain resources or decorations for you. The rarest monster materials can be bought with special tickets that you typically earn when you complete all of your weekly limited bounties. These limited bounties are automatically picked up the first time you visit the resource center for that week.

Note: During festivals, such as the one going on right now for the next 3 weeks, limited bounties are daily, so you get a new set every day.

[RemnantHelmet]

Originally posted by Suzaku:

Special investigations are just story-based stuff. They don't really matter for what you're looking for.

Investigations are unlocked randomly when you pick up tracks and break monster parts. The investigation you're given is based on the locale. The monster(s) of the investigation is randomized within that locale, so you might pick up tracks in the forest from Tobi, but the investigation it spawns could be to fight a Rathalos in the forest.

The Melder can make certain resources or decorations for you. The rarest monster materials can be bought with special tickets that you typically earn when you complete all of your weekly limited bounties. These limited bounties are automatically picked up the first time you visit the resource center for that week.

Note: During festivals, such as the one going on right now for the next 3 weeks, limited bounties are daily, so you get a new set every day.

Do I have to register these? On my limited bounty list there are two tabs with just question marks and no bounty details, how do I unlock these? Do I get the reward when I finish all of these today?

[Nope]

Originally posted by Norman Casque Nathan:

Originally posted by Suzaku:

Special investigations are just story-based stuff. They don't really matter for what you're looking for.

Investigations are unlocked randomly when you pick up tracks and break monster parts. The investigation you're given is based on the locale. The monster(s) of the investigation is randomized within that locale, so you might pick up tracks in the forest from Tobi, but the investigation it spawns could be to fight a Rathalos in the forest.

The Melder can make certain resources or decorations for you. The rarest monster materials can be bought with special tickets that you typically earn when you complete all of your weekly limited bounties. These limited bounties are automatically picked up the first time you visit the resource center for that week.

Note: During festivals, such as the one going on right now for the next 3 weeks, limited bounties are daily, so you get a new set every day.

Do I have to register these? On my limited bounty list there are two tabs with just question marks and no bounty details, how do I unlock these? Do I get the reward when I finish all of these today?

The ??? Mean you haven't encounter the requested monster yet