If you want to count the number of cells in a specific column of a datatable that are not blank/empty, you can use the following:
dt1.AsEnumerable().Where(function(r) Not(String.IsNullOrWhiteSpace(r.Item("oden de pedido").ToString))).Count
This uses linq/lambda. How it works is that it converts all of the rows in the column “oden de pedido” to string, then checks to see if that row is null, blank, or has whitespace characters only. This is all contained in a .Where() statement, so it only selects datarows where the expression to the right of the Where statement is true. Since I put the Not() operator at the beginning, it is grabbing all datarows that are NOT blank, empty, or whitespaces. Then it counts how many rows were grabbed and returns it as an integer.