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Relative Clauses 2

Let's do it case by case then.

1.Quem
O cara quem te ameaçou ontem (es)tá morto já.
(The guy who threatened you yesterday is dead already.)
O cara que te ameaçou ontem (es)tá morto já.
(The guy that threatened you yesterday is dead already.)

2.Onde
O lugar onde (eu) fui criado é tão lindo.
(The place where I've been raised is so beautiful.)
O lugar em que (eu) fui criado é tão lindo.
(The place that I've been raised in is so beautiful.)

3. Quando
Aquele momento quando os pais sorriem para ti é tão mágico.
(That moment when the parents smile for you is so magic.)
Aquele momento (em) que os pais sorriem para ti é tão mágico.
(That moment that the parents smile for you is so magic.)

4. Qual
Aquele exame o qual (eu) fiz ontem foi tão fácil.
(That exam which I made yesterday was so easy.)
Aquele exame que (eu) fiz ontem foi tão fácil
(That exame that I made yesterday was so easy.)

Except for 'quem', that can be very elusive within formal/written records, all others are universally present and correct. You tend to use 'which' more than we use 'qual' too.
Also, where a preposition and/or article is supposed to be demanded, we have multiple options... That commonly are ignored: people oftenly skip them.