As layout is no difference, but you can look for hints.
Locate in statement deposits/withdrawals/bonuses. A demo account will have only a starting deposit and no withdraw or bonus.
Account number: demo accounts have much higher number as real accounts.
( example:demo 7 digits account number while real accounts have 4 digits)
If you don’t know real accounts number, open a demo on that broker and see if your new demo is near to that statement account number.
Is account name listed? if yes should be name of a person or company.(not much help as on demo can open with any name but a clue owner do not want to hide his name)
Is statement complete? If is not and is listing last trades only it no matter if is real or demo, skip it