The first round was a phone screen with an HR person. They asked why you applied for that specific role and how your background is relevant to the job. They also asked why MongoDB, what was the hardest/most interesting project or problem you've worked on, and other normal interview questions.

The next round was a phone interview with an engineer. They asked more about your background and whether or not you've used MongoDB in a project or their new serverless platform. You'll also be given an algorithms question related to a feature or the way the database itself works.

Ensure you really know the ins and outs of how this NoSQL database works under the hood and have used it in a project before. They will ask questions about it, no matter how obscure. There doesn't seem to be a huge penalty for not knowing, but it certainly helps to know because it gets the explanation out of the way fast. Also, really listen to the question because there is a lot of setup.

Make sure you know your recursion and string manipulation type questions.

I only remember this question vaguely.

It was a question about projections of collections and printing out documents and subdocuments.

It might have had to do with match or find on MongoDB.