@Patience_George You have to do some custom scripting to fetch leave without pay days on change of employee or month of salary and for deduction of salary you can tick “Depends on Leave Without Pay” checkbox in salary structure of that employee. “Depends on Leave Without Pay” checkbox will be in earning and deduction child tables.
@Patience_George You have to customize according to your need. you can go through documentation of customization of erpnext. or study the existing code how calls and events work.