Can employee mark Multiple In-Out?

Yes, It is possible for your employees to punch multiple times.
Based on your company’s policy you can enable/disable multiple punch policy:
Go to Settings > Attendance Settings > Attendance Configuration > “Time spent calculated based on first In and last Out”.

If it is enabled, it would calculate total time from first In punch to last Out Punch.
Example:
First In- 10 am
First Out- 11 am
Second In- 12 pm
Second Out- 1 pm
Then, Total Time= 3 hours

If it is disabled, it would only calculate the the total In Time from first In punch to last Out Punch.
Example:
First In- 10 am
First Out- 11 am
Second In- 12 pm
Second Out- 1 pm
Then, Total Time= 2 hours