It would be very unusual for strangers to create a username for someone.
Student or Learner
Lets say my name is John, and facebook.com/john is taken, what other name suggestions do you have? Prefer something easy and professional.
One problem with a very common name like John is that there will be hundreds of variations around it and it will be difficult to find something simple using it. How common is your surname?
I mean I am asking if there is any prefix or suffix that is suitable.
For example: facebook.com/johnfb , /johnplace, /happyjohn /sunnyday
I don't use Facebook, but most site that require usernames are generally the same - you can use anything you want, as long as it's not already taken and it meets any character/length requirements of the site. Some may have restrictions on obscenities or profanities in the username as well.
Sometimes people try alternate phonetic spellings of a name to make it more original to decrease chances of it already being taken - Jawn, Gean, Jahan. Maybe translate it into the equivalent in another language, Ivan, Johan, Juan, etc.
There isn't any style standards for usernames, if that's what you're asking. As long is it meets requirements and isn't taken, go for it.