DispatchGroup

You can use integrate DispatchGroup on execute method.

ExampleService.swift

import VFNetwork
import Foundation

class HomeService: RequestService<HomeAPI> {
    
    let group = DispatchGroup()
    
    func getJokes(completion: @escaping (Result<HomeModel, Error>, _ group: DispatchGroup) -> Void) {
        execute(.home, responseType: HomeModel.self, group: group, completion: completion)
    }
    
    func getCategories(completion: @escaping (Result<HomeCategories, Error>, _ group: DispatchGroup) -> Void) {
        execute(.categories, responseType: HomeCategories.self, group: group, completion: completion)
    }
}

and execute in your viewModel using leave() to terminate group independent execution.

ExampleViewModel.swift

    func getJokes(completion: @escaping (Result<HomeModel, Error>) -> Void) {
        service.getJokes { result, group in
            group.leave()
            switch result {
            case let .success(joke):
                completion(.success(joke))
            case let .failure(error):
                completion(.failure(error))
            }
        }
    }
    
    func getCategories() {
        service.getCategories { result, group in
            group.leave()
            switch result {
            case let .success(categories):
                break
            case let .failure(error):
                print(error)
            }
        }
    }

in your ViewController intercept your group to receive action when your group is finish.

ExampleViewController.swift

    func fetch() {
        viewModel.getJokes { result in
            switch result {
            case let .success(jokes):
                break
            case let .failure(error):
                debugPrint(error)
            }
        }
        
        viewModel.getCategories()
        
        viewModel.service.group.notify(queue: .main) {
            print("Services Finished.")
        }
    }