public class ChangeLog
{
    public int ChangeLogId { get; set; }

    public string Description { get; set; }

    public Audit Audit { get; set; }
}

[Owned]
public class Audit
{
    [Column(nameof(ChangedBy))] // for setting custom column name, in this case prefix OwnedType_ ('Audit_') removed, so column would be only ('ChangedBy')
    public string ChangedBy { get; set; } // default Column name for Property of OwnedType is OwnedType_Property ('Audit_ChangedBy')

    public bool IsDeleted { get; set; }

    [NotMapped] // alternatively in OnModelCreating(): modelBuilder.Entity<Audit>().Ignore(a => a.ChangedTime);
    public DateTime? ChangedTime { get; set; }

    // Added owned type property
    public AuditExtended AuditExtended { get; set; }
}

[Owned]
public class AuditExtended
{
    [Required] // Added required so if fails on null insert
    public string CreatedBy { get; set; }

    [NotMapped]
    public DateTime? CreatedTime { get; set; }

    [NotMapped]
    public string Remark { get; set; }
}