where the jetstream route is placed

They are listed in the ServiceProvider of JetStream package itself.

Here you go: https://github.com/laravel/jetstream/blob/1.x/src/JetstreamServiceProvider.php#L168-L178

where is it triggered so that the route can be registered in the app? basically I want to adjust the auth feature on jetstream.

jetstream routes are not listed in routes / web.php but they do. and he exists only in the root domain.

for example in laravel ui I can call Auth: routes () across multiple domain groups.

Route::domain('sub1.example.dev')->group( function () {
	Auth:routes();
	.....
});

Route::domain('sub2.example.dev')->group( function () {
	Auth:routes();
	.....
});

I found it in vendor/laravel/fortify/routes/routes.php, but how / where is this called?

You will find how it's called here: /vendor/laravel/fortify/src/FortifyServiceProvider.php. Booted through the service provider.

To override the URL paths for login, logout and register you will need to make the following adjustments in your fortifyserviceprovider.php:

//add this code to the register method
Fortify::ignoreRoutes();  

After adding the ignoreroutes you could copy and use the routes defined in /vendor/laravel/fortify/routes/routes.php as a starting point to your web.php file

@ekrist1 is correct here.

This is a different approach than Laravel UI, but it's also a different auth system ;)

I will be appreciated if you help me with routes of laravel 8 app. The case is that after I installed jetstream I saw new routes as author mentioned, but now /routes/web.php does not react if I put any other route in there.

Is there any other place I should place any new routers I need?

Should I place it all in /vendor/laravel/fortify/routes/routes.php?

I do not need to override the URL paths for login, logout and register but I did't get the way to make a routing with Jetstream.

@dzendigital put your routes in web.php as before but note that the syntax has changed and you niw need to specify the full class path

Thank you for your answer.