C#

public static IReadOnlyCollection<T> FindPath<T>(this IReadOnlyDictionary<T, IReadOnlyCollection<T>> nodes, T start, T target, IEqualityComparer<T> comparer = null)
{
    if (nodes == null) throw new ArgumentNullException(nameof(nodes));
    if (comparer == null) comparer = EqualityComparer<T>.Default;
    
    var prefix = new List<T> { start };
    return FindPathCore(start, prefix);

    IReadOnlyCollection<T> FindPathCore(T current, IReadOnlyCollection<T> pathToCurrent)
    {
        if (comparer.Equals(current, target))
        {
            return pathToCurrent;
        }
        if (nodes.TryGetValue(current, out var connections))
        {
            foreach (T node in connections.Except(pathToCurrent))
            {
                var path = new List<T>(pathToCurrent);
                path.Add(node);
                var result = FindPathCore(node, path);
                if (result != null) return result;
            }
        }
        
        return null;
    }
}

var test5 = new Dictionary<string, IReadOnlyCollection<string>>
{
    ["a"] = new List<string> { "c", "d", "b" },
    ["b"] = new List<string> { "c", "f", "g", "e" },
    ["e"] = new List<string> { "g", "h", "k" },
    ["k"] = new List<string> { "b", "l" },
};

test5.FindPath("a", "d").Dump(); // a d
test5.FindPath("a", "f").Dump(); // a b f
test5.FindPath("a", "k").Dump(); // a b e k
test5.FindPath("k", "x").Dump(); // null
test5.FindPath("k", "g").Dump(); // k b g

Pete O'Hanlon wrote:

also, you need to learn how to read a build error; this was all clearly laid out

var companyId = 100; //set some value

var contacts = (from a in db.Company
                 join b in db.CompanyContacts on a.CompanyId equals b.CompanyId
                 join c in db.Contacts on b.ContactId equals c.ContactId
                 where a.CompanyId == companyId
                 select(x => new ContactEntity
                        {
                            Id = x.Id,
                            Prefix = x.Prefix,
                            FirstName = x.FirstName,
                            MiddleName = x.MiddleName,
                            LastName = x.LastName,
                            Suffix = x.Sufffix
                   }));