What are two examples/quotes that show the Nurse to be both witty toward and supportive of Juliet's relationship with Romeo in Romeo and Juliet?
I recommend looking at Act II, scene v for the best quotes. In this scene, Juliet is waiting to hear how the Nurse's discussion went with Romeo regarding when they are going to get married.
The Nurse says to Juliet in jest:
Well, you have made a simple choice; you know not
how to choose a man: Romeo! no, not he; though his
face be better than any man's, yet his leg excels
all men's; and for a hand, and a foot, and a body,
though they be not to be talked on, yet they are
past compare: he is not the flower of courtesy,
but, I'll warrant him, as gentle as a lamb. Go thy
ways, wench; serve God. What, have you dined at home?
Here the Nurse teases Juliet about who she has fallen in love with essentially saying, "Sure he's handsome, but he's really not all that!" And then, the Nurse still doesn't answer Juliet's original question. She has now ignored it several times. Her ability to come up with quick ways to change the topic makes her a witty character. In these words, the Nurse demonstrates approval for Romeo and his looks, while at the same time messes with Juliet about the entire idea of a relationship with him.
Then, the Nurse FINALLY asks Juliet if she can go to confession today. Juliet says she can. So the Nurse then states:
There stays a husband to make you a wife:
Now comes the wanton blood up in your cheeks,
They'll be in scarlet straight at any news.
Hie you to church; I must another way,
To fetch a ladder, by the which your love
Must climb a bird's nest soon when it is dark:
I am the drudge and toil in your delight,
But you shall bear the burden soon at night.
Here the Nurse tells Juliet that Romeo will be waiting for her at the church. She then goes into how "hot" it is going to make Juliet to feel like she gets to have Romeo in more than one sense of the verb. On the one hand she will at that point be married to Romeo and therefore possess him. On the other hand, she will legally be able to have him in the biblical sense... in a bedroom.
The Nurse references with the word "burden" two meanings. Burden usually means a pain, but for Juliet it will be the joy of the physical expression of love that she will get from Romeo after the Nurse helps arrange for a ladder so Romeo can climb up and be with Juliet later that evening.