C# solution

public static string pangrams(string s)
{
    var lowerString = s.ToLower();
    char[] characters = lowerString.ToCharArray().Where(e => !string.IsNullOrEmpty(e.ToString().Trim())).ToArray();

    var charList = new List<char>();
    foreach(var character in characters)
    {
        if(charList.Any(e => e == character))
            continue;

        charList.Add(character);
    }

    if(charList.Count == 26)
        return "pangram";

    return "not pangram";
}