After market close today, Facebook (NASDAQ:FB) will report fourth-quarter earnings. While investors will undoubtedly be interested in the data provided in the quarterly earnings report, some of the most useful nuggets may be gleaned from the earnings call following the release. Here are three questions analysts will likely ask Facebook CEO Mark Zuckerberg.

Is Snapchat a threat?
Facebook-buyout-offer-turned-sour Snapchat continues to turn up the volume. In the social app company's latest round of funding, the company was valued at $10 billion. Not only is the company growing rapidly, reportedly approaching 200 million monthly active users, but it also seems to be attempting to create a portal of its own in an attempt to get more attention from users throughout the day, a move that could impact Facebook if it successfully keeps users in its app longer.

Snapchat isn't just a chat app anymore. In November, Snapchat debuted Snapcash, a way for users to transfer money to other users without any fees. And just this week Snapchat announced Snapchat Discover, a new section of its app that features news, music, and other content. Snapchat Discover is a clear attempt to get users to spend more time in the Snapchat app.

Snapchat Discover. Image source: Snapchat.

Some Facebook investors may wonder whether Zuckerberg sees Snapchat as a threat or not. And if Snapchat is, indeed, competition, is Facebook confident it can protect its user base from the fast-growing app?

How big is the revenue stream from Instagram?
"Over the next five years our goals are around taking our next generation of services -- Instagram, Messenger, WhatsApp, and search -- and helping them connect billions of people and become important businesses in their own right," Zuckerberg said during the company's most recent earnings call. The most meaningful contributor of these three to Facebook's business is almost certainly Instagram.

But just how big is the potential with this app, investors wonder?

During the Q3 call, Facebook Chief Operating Officer Sheryl Sandberg said the social network will "continue to roll out ads on Instagram ... but we're going to remain deliberate and slow in our approach to scaling [this ad business]."

Instagram app. Image source: Instagram.

As Instagram grows larger, Facebook may choose to provide concrete numbers on revenue from Instagram. Could we finally see some financial figures on Instagram today?

How is the new Facebook ad network performing?
Facebook is an advertising behemoth, raking in $2.96 billion in advertising revenue in Q3 alone -- and that figure was up a whopping 64% from the year-ago quarter. But most of this revenue comes from paid advertising for ads on Facebook's web properties. As of October, however, Facebook opened up its ad network that allows advertisers to purchase Facebook ads and display them on third-party apps to all of Facebook's advertisers. More details on the early progress of this ad network would be useful.

The implications of Facebook competing in the ad network business are huge. Not only does it open up an entirely new revenue stream for Facebook, but it also enables the company to compete with Google's ad network. Will Facebook's approach of using Facebook user data for ad targeting prove able to hold its own against Google's ad network empire?

For a preview of the key metrics to watch when Facebook reports earnings today, check out this Foolish earnings preview.

Wondering how to get access to the earnings release and listen to the call for yourself? Shortly after market close, Facebook's fourth-quarter results will be published here. Tune into Facebook's live conference call at 5:00 PM ET here.

Check back at The Motley Fool at for a Foolish take on Facebook's fourth-quarter results.