Creating a grid in HTML from a database search

Use string.Empty instead of "" to indicate an empty string. It conveys your intent without ambiguity (i.e.: nobody will think you forgot to enter something in the string).

When concatenating in a loop, use a StringBuilder.

Use meaningful names. I don't know what concat and oDrc actually mean. Nor pkunica, but that might be a language-issue (I'd encourage you to stick to English-only).

Your first loop is unnecessary, you add more code, and more complexity, by making it a loop, and remove nothing. A loop where the loop control variable is unused should be suspect.

You are repeating yourself, and in the process making your code harder to read.

if (concat != "")
        {
            concat += "," + oDrc[y].ItemArray[i].ToString().Trim().Replace("'", "");
        }
        else
        {
            concat += oDrc[y].ItemArray[i].ToString().Trim().Replace("'", "");
        }

Should be:

if (!string.IsEmptyOrNull(concat))
{
    concat += ","; // except using a stringbuilder
}
concat += oDrc[y].ItemArray[i].ToString().Trim().Replace("'", "");

It is then clear that the action is the same.

Always try to do as much as possible in the common code, and not duplicate code between branches.

(Given how your code looks and the fact you are talking about database searches, I will assume oDrc[y] is a DataRow object)

If you are using .NET 4, you can use LINQ and string.Join:

Using the following helper methods:

private static string GetRowString(DataRow row, int count)
{
    var rowItems = row.ItemArray.Take(count);
    return string.Join(",", rowItems.Select(GetReadableString));
}

private static string GetReadableString(object item)
{
    return item.ToString().Trim().Replace("'", string.Empty);
}

your new method body becomes:

var count = pkunica ? 2 : Pks.Length;
var concat = GetRowString(oDrc[y], count);