We are talking about time here. 'En' is used in a similar way to 'in' in English - en hiver -in Winter, en septembre - in September, en semaine - in(or at some time in) the week (on weekdays if you prefer). Pendant means during or for the duration of - 'pendant une semaine' means for a week (ie during the whole week) -'pendant ce temps-là' is a way of saying meanwhile (during that time).
Quelle est ta leçon préférée? means - what (or which) is your favourite lesson?
de quelle couleur est-ce / est-il / est-elle ? -
"Il est quelle heure" means "What time is it?" in French.
"est de quelle nationalité ?" is a question asking about citizenship. You can typically find that on legal or administrative forms (state your country of nationality)
"il est [heure]" (it is [time])
Vingt km
what is the diference biteween jupiter and the sun
distance = 137 km driving time = 02H10
Which is the distance between Montreal and British Colombia?
C'est la température d'auto-ignition
Environ 34 km, entre Douvres et le cap Blanc-Nez
quelle heure est-il ? However nowadays we prefer to say 'have you got the time?' in French too rather than quelle heure est-il: Vous avez l'heure? Tu as l'heure? are more commun.
Quelle est ton nationalite means 'What is your nationality'
"quelle couleur est-ce ?"de quelle couleur est cet objet ? : what colour is that object?
Il est quelle huere? (What time is it)
What is the date? is the translation for Quelle est la date.
'mais quelle est cette ...' means but what is this (thing) / who is this (person).