Try signing out and signing in again. If that doesn't work for some reason, sign out, close your browser, open up the main page, sign in, and then find the question again; you should be logged in and able to see it. If this still doesn't work, try contacting Brainly's tech support:
https://brainly.com/contact/index
EDIT:
This is all under the assumption you have actually successfully made an account.
