public static List<int> GetHasValueRowIndex(string[,] arr)
{
    var hasValueRowIndex = new List<int>();
    for (var i = 0; i < arr.GetLength(0); i++)
    {
        for (var j = 0; j < arr.GetLength(1); j++)
        {
            if (!string.IsNullOrEmpty(arr[i, j]))
            {
                hasValueRowIndex.Add(i);
                break;
            }
        }
    }
    return hasValueRowIndex;
}

//Demo

string[,] a = new string[9, 3];
a[0, 0] = "a";
a[2, 0] = "b";
a[4, 0] = "c";
a[6, 0] = "d";
a[8, 0] = "e";

var arr = GetHasValueRowIndex(a);
Console.WriteLine("HasValue Row Count:" + arr.Count);
arr.ForEach(o => Console.WriteLine(o));
/*
 HasValue Row Count:5
 0
 2
 4
 6
 8
 */