I tried below code: [But didn't work]
alert('Is Checked : ' + BulkSelectName.checked);
So it is better to use class selectors instead. Assuming that the header of your Table Records is the default TableRecords_Header, you can use the following code to reach the List_BulkSelect in the header:
So your example can become:
alert('Is Checked : ' + $('.TableRecords_Header input').checked);
I hope this helps.