Here below is a personnel data table:

To count the number of duplicate data (the judging basis is that the data in the Name field are the same), enter the formula in the cell E2:

=spl("=?1.conj().select(~==?2).count()",B$2:B$7,B2)

Then drag E2 down to every relevant row:

esProc Desktop and Excel Processing
9.4 Count number of repetitions of simple members
9.6 Count number of repetitions of row-based data - by whole row