Help me pls... Why when I run the, I didn't see the answer

Taking Richard's cue, we could try:

#include<iostream>
  
using namespace std;

int main()
{
  int detik;
  int menit;
  int jam;
  int total_detik;
  int sisa;

  cout << " ======Hitung waktu====== " << endl;
  cout << " masukkan total detik :";
  cin >> total_detik;

  jam = total_detik / 3600;
  sisa = total_detik % 3600;
  menit = sisa / 60;
  detik = sisa % 60;

  cout << " Jadi, " << total_detik << " detik adalah sama dengan " << jam << " jam " << menit << " menit " << detik << " detik\n";

  // wait for user input
  cin.ignore(256, '\n');
  cin.get();
}

Quote:

I tried all day , please help me. I can't see the answer when I run.

In your question you didn't told if answer is wrong or if nothing is printed or if screen is cleaned before you see what the program printed and if it printed anything.
- add checkpoints in your program, to ensure the execution reached certain point.

#include<iostream>

using namespace std;

int main()
{
	int detik;
	int menit;
	int jam;
	int total_detik;
	int sisa;
	
	cout << "Checkpoint: Program Start";
	cout << " ======Hitung waktu====== " <<endl;
 cout="" <<="" "="" masukkan="" detik="" :";
="" cin="">> detik;
	
	jam = total_detik / 3600;
	sisa = total_detik % 3600;
	menit = sisa / 60;
	detik = sisa % 60;
	cout << "Checkpoint: Calculation done";	

	cout << " Jadi, " << total_detik << " detik adalah sama dengan " << jam << " jam " << menit << " menit " << detik << " detik ";
	
	cout << "Checkpoint: Program End";
	return 0;
	}

- Use the debugger to investigate what is going on in your program.
Your code do not behave the way you expect, or you don't understand why !

There is an almost universal solution: Run your code on debugger step by step, inspect variables.
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't know what your code is supposed to do, it don't find bugs, it just help you to by showing you what is going on. When the code don't do what is expected, you are close to a bug.
To see what your code is doing: Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.

Debugger - Wikipedia, the free encyclopedia[^]

Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
Basic Debugging with Visual Studio 2010 - YouTube[^]

1.11 — Debugging your program (stepping and breakpoints) | Learn C++[^]

The debugger is here to only show you what your code is doing and your task is to compare with what it should do.

Look at your code:

#include<iostream>


	int detik;
...
	int total_detik;
...
    cin="">> detik;
	
	jam = total_detik / 3600;
	sisa = total_detik % 3600;
	menit = sisa / 60;
	detik = sisa % 60;
	
	cout << " Jadi, " << total_detik << " detik adalah sama dengan " << jam << " jam " << menit << " menit " << detik << " detik ";
	
	return 0;
	}

Between declaring it and using it's content, you don't give total_detik any value at all.
You read a value into detik, but you don't use it!
Try changing this line:

cin >> detik;

To this:

cin >> total_detik;

And see what happens.

To be honest, if you'd followed the advice you were given ages ago and used the debugger, you would have seen exactly what was going on.
The debugger is your friend: it's much faster than asking others to solve it for you ...