create enum with string

export class ProcessTypeEnum
{
  public static readonly Appeal = "Appeal";
  public static readonly CourseProgress = "Course Progress";
  public static readonly WelfareManagement = "Welfare Management";
  public static readonly IecDurationChange = "Change IEC Duration";
  public static readonly Attendance = "Attendance";
  public static readonly CompletionStudyAbroad = "Completion-Study Abroad";
  public static readonly Withdrawal = "Withdrawal";
  public static readonly Suspension = "Suspension";
  public static readonly SchoolYearChange = "School Year Change";
  public static readonly TerminateCourse = "Terminate Course";
  public static readonly LeaveManagement = "Leave Management";
  public static readonly CompletionISP = "Completion-ISP";
  public static readonly ATEManagement = "ATE Management";
  public static readonly SchoolInterview = "School Interview";
  public static readonly IECorSchoolPlacement = "IEC or School Placement";
  public static readonly IECtoSchoolTransition = "IEC to School Transition";
  public static readonly IECorSchoolTransfer = "IEC or School Transfer";
  public static readonly COEManagement = "COE Management";
  public static readonly PlacementSuitability = "Placement Suitability";
  public static readonly PNH = "PNH";
}

export const PROCESS_NAMES = {
    ATE_MANAGEMENT: 'ATE Management',
    PLACEMENT: 'IEC or School Placement',
    APPEAL: 'Appeal',
    COURSE_PROGRESS: 'Course Progress',
    WELFARE_MANAGEMENT: 'Welfare Management',
    IEC_DURATION_CHANGE: 'Change IEC Duration',
    ATTENDANCE: 'Attendance',
    COMPLETION_STUDY_ABROAD: 'Completion-Study Abroad',
    WITHDRAWAL: 'Withdrawal',
    SUSPENSION: 'Suspension',
    SCHOOL_YEAR_CHANGE: 'School Year Change',
    TERMINATE_COURSE: 'Terminate Course',
    LEAVE_MANAGEMENT: 'Leave Management',
    COMPLETION_ISP: 'Completion-ISP',
    SCHOOL_INTERVIEW: 'School Interview',
    IEC_SCHOOL_TRANSITION: 'IEC to School Transition',
    IEC_SCHOOL_TRANSFER: 'IEC or School Transfer',
    COE_MANAGEMENT: 'COE Management',
    PLACEMENT_SUITABILITY: 'Placement Suitability',
    IEC_ASSESSMENT: 'IEC Assessment',
    COMPLETION_BOTH: 'Completion'
}

create model with class

import { NoteDTO } from '../notes/create-notes';

export class WorktrayItem {
  WorkTrayId: string;
  ProcessRequestId: string;
  ProcessTypeId: string;
  ProcessName: string;
  StudentNumber: string;
  StudentId: string;
  FamilyName: string;
  GivenName: string;
  Nationality: string;
  NationalityCountryId: string;
  DateOfBirth: Date | null;
  Gender: string;
  Program: string;
  SchoolYear: number;
  RelatedSchoolId: string;
  Agent: string;
  HomeStayProvider: string;
  Status: string;
  ProcessStatus: string;
  Description: string;
  ModifiedDate: Date;
  WarningDate: Date | null;
  ExtensionData: { [key: string]: string };
  WorkTrayItemType: string;
  IsAnyNotes: boolean;
  IsUnReadNotesAvailable: boolean;
  Notes: NoteDTO[];
  EnrolmentDate: Date | string | null;

  CountryOfBirthId: string;
  CountryOfBirth: string;
  DisplayOrder: number;
  DeCaseOfficer: string;

  NeedReAcknowledgement: boolean;
  ProcessAllWorkTrayItemIdList: string[];

  AssignedStaffId: string;

  constructor(worktrayItem: WorktrayItem | any) {
    this.WorkTrayId = worktrayItem.WorkTrayId;
    this.ProcessRequestId = worktrayItem.ProcessRequestId;
    this.ProcessTypeId = worktrayItem.ProcessTypeId;
    this.ProcessName = worktrayItem.ProcessName;
    this.StudentNumber = worktrayItem.StudentNumber;
    this.StudentId = worktrayItem.StudentId;
    this.FamilyName = worktrayItem.FamilyName;
    this.Nationality = worktrayItem.Nationality;
    this.NationalityCountryId = worktrayItem.NationalityCountryId;
    this.GivenName = worktrayItem.GivenName;
    this.DateOfBirth = worktrayItem.DateOfBirth;
    this.Gender = worktrayItem.Gender;
    this.Program = worktrayItem.Program;

    if (worktrayItem.SchoolYear !== null) {
      if (worktrayItem.SchoolYear.toString().toLowerCase() === 'kindergarten') {
        this.SchoolYear = 0;
      } else {
        this.SchoolYear = isNaN(worktrayItem.SchoolYear) ? Number(worktrayItem.SchoolYear.slice(4)) : Number(worktrayItem.SchoolYear);
      }
    } else {
      this.SchoolYear = 0;
    }

    this.RelatedSchoolId = worktrayItem.RelatedSchoolId;
    this.Agent = worktrayItem.Agent;
    this.HomeStayProvider = worktrayItem.HomeStayProvider;
    this.Status = worktrayItem.Status;
    this.ProcessStatus = worktrayItem.ProcessStatus;
    this.Description = worktrayItem.Description;
    this.ModifiedDate = worktrayItem.ModifiedDate;
    this.WarningDate = worktrayItem.WarningDate;
    this.ExtensionData = worktrayItem.ExtensionData;
    this.WorkTrayItemType = worktrayItem.WorkTrayItemType;
    this.IsAnyNotes = worktrayItem.IsAnyNotes;
    this.IsUnReadNotesAvailable = worktrayItem.IsUnReadNotesAvailable;
    this.Notes = worktrayItem.Notes;
    this.CountryOfBirthId = worktrayItem.CountryOfBirthId;
    this.CountryOfBirth = worktrayItem.CountryOfBirth;
    this.DisplayOrder = Number(worktrayItem.DisplayOrder);
    this.DeCaseOfficer = worktrayItem.DeCaseOfficer;

    this.AssignedStaffId = worktrayItem.AssignedStaffId;

    this.NeedReAcknowledgement = worktrayItem.NeedReAcknowledgement;
    this.ProcessAllWorkTrayItemIdList = worktrayItem.ProcessAllWorkTrayItemIdList;
  }
}

Dictionary in Angular

C#: public Dictionary<string, string> ExtensionData { get; set; }

Angular Model: ExtensionData: { [key: string]: string };

Implementation: this.worktrayItem.ExtensionData.SchoolTerm