Depending on which position you interview for and your background, questions asked could vary. But in general, first round is phone/video interview and second round is a half-day on-site 'superday' consists of 4-6 rounds of one-on-one interviews.
Be prepared to answer the following behavioral questions:
(1) Why BlackRock? Try organize your answer around BlackRock values (One BlackRock, fiduciary etc.)
(2) Why this team/position
The technical questions may vary from market question (e.g. are you following the market? Tell me an interesting piece of market news you came across) to finance questions (e.g. bond pricing, derivatives).
In summary, make sure you prepare to answer questions about details on your resume and familiarize yourself with market news/finance terms - you'll be fine!
The interviews I underwent for this role were not as tough as you would think. They are just looking for a certain type of person. You need to show them that you are personable and that you are interested and keeping up with the markets. They want to ultimately see that you can eventually become an internal wholesaler for them.
Just be yourself. Be frank, learn about the organizations, try to connect with different people to atleast get an idea of the role you are applying to, so that way you wouldn't be completely lost during your interview. if you are still not sure, of what is expected of you, don't be afraid to ask more questions. Interviews are just a formal chat!