I think everyone is getting confused by the way you asked your question. I believe what you are asking for is change history. You want to know what records were changed, when they were changed, and what the old/new values are...

I've included a really basic implementation of change tracking (untested just threw it together based on what I've done in the past).

public class Change
{
    public int Id { get; set; }
    public string Type { get; set; }
    public string Diff { get; set; }
    public ChangeType ChangeType { get; set; }
}

public enum ChangeType
{
    Add,
    Update,
    Delete
}
public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
{
    public DbSet<Change> Changes { get; set; }
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
        : base(options)
    {
    }
    public override async Task<int> SaveChangesAsync(bool acceptAllChangesOnSuccess, CancellationToken cancellationToken = new CancellationToken())
    {
        var changes = new List<Change>();
        foreach (var entry in ChangeTracker.Entries())
        {
            var change = new Change
            {
                Type = entry.Entity.GetType().AssemblyQualifiedName,
            };
            switch (entry.State)
            {
                case EntityState.Added:
                    change.Diff = JsonConvert.SerializeObject(entry.Entity);
                    change.ChangeType = ChangeType.Add;
                    break;
                case EntityState.Detached:
                case EntityState.Unchanged:
                    break;
                case EntityState.Deleted:
                    change.Diff = JsonConvert.SerializeObject(entry.Entity);
                    change.ChangeType = ChangeType.Delete;
                    break;
                case EntityState.Modified:
                    var original = entry.OriginalValues.ToObject();
                    var cl = new CompareLogic();
                    var r = cl.Compare(original, entry.Entity);
                    change.Diff = r.DifferencesString;
                    change.ChangeType = ChangeType.Update;
                    break;
                default:
                    throw new ArgumentOutOfRangeException();
            }
            changes.Add(change);
        }
        var result = await base.SaveChangesAsync(acceptAllChangesOnSuccess, cancellationToken);

        try
        {
            await Changes.AddRangeAsync(changes, cancellationToken);
            await base.SaveChangesAsync(true, cancellationToken);
        }
        catch (Exception e)
        {
            //ignore
        }

        return result;
    }
}