What is the Halacha of putting on a new pair of Tzitzit on Shabbat afternoon? Does one need to make a new Bracha? How about after taking a shower or nap?

A new Talit Katan requires a new Bracha (SA OC 8, 12-13). For re-wearing the Talit Katan after a nap or a shower, if you had the intention to re-wear, no Bracha is needed; if you had no intention, a new Bracha in required. (see ibid 14)