using System;

using System.Collections.Generic;

using System.Linq;

​

// https://stackoverflow.com/questions/59621091/ef-core-3-0-convert-sql-to-linq

public class Program

{

    public static void Main()

    {

        var enrollments = new List<Enrollments>

        {

            new Enrollments { StudentId = 1, CourseId = 1 },

            new Enrollments { StudentId = 1, CourseId = 2 },

            new Enrollments { StudentId = 1, CourseId = 3 },

            new Enrollments { StudentId = 1, CourseId = 4 },

            new Enrollments { StudentId = 1, CourseId = 5 },

            new Enrollments { StudentId = 1, CourseId = 6 },

            new Enrollments { StudentId = 2, CourseId = 1 },

            new Enrollments { StudentId = 2, CourseId = 2 },

            new Enrollments { StudentId = 2, CourseId = 3 },

            new Enrollments { StudentId = 2, CourseId = 4 },

            new Enrollments { StudentId = 2, CourseId = 5 },

        };

        var courses = new [] {1, 2, 3, 4, 5};

        var groupedEnrollment = enrollments.GroupBy(p => p.StudentId)

                                            .Select(g => new 

                                            {

                                                StudentId = g.Key,

                                                Courses = g.Select(p => p.CourseId).ToArray() 

                                            });

        var result = groupedEnrollment.Where(g => 

                                             g.Courses.Length == courses.Length &&

                                             g.Courses.Intersect(courses).Count() == courses.Length);

        foreach(var item in result)

            Console.WriteLine(item.StudentId);

    }

    public class Enrollments 

    {

        public int StudentId { get; set; }

        public int CourseId  { get; set; }

    }

}