is there a way to number all 64 squares? So all squares have a number on them
A number on them? Yea, there's lots of ways. Here's one:
01-02-03-04-05-06-07-08
09-10-11-12-13-14-15-16
17-18-19-20-21-22-23-24
25-26-27-28-29-30-31-32
33-34-35-36-37-38-39-40
41-42-43-44-45-46-47-48
49-50-51-52-53-54-55-56
57-58-59-60-61-62-63-64
Here's another:
81-82-83-84-85-86-87-88
71-72-73-74-75-76-77-78
61-62-63-64-65-66-67-68
51-52-53-54-55-56-57-58
41-42-43-44-45-46-47-48
31-32-33-34-35-36-37-38
21-22-23-24-25-26-27-28
11-12-13-14-15-16-17-18
(file, row)
In this numbering format, square 84, for example, is the 8th row, 4th file, from White's point of view.
Though as Stephen mentioned, it's hard to beat algebraic.
that notation places a piece on the board so if I want to replace that piece with a number does fen allow that?