as salam alaikum
the 'awrah of a believer should be covered during salat. According to the opinion of the vast majority of Imami Shia scholars the 'awrah of a Muslim male includes the pudendal area. However it is disliked to show any parts from the navel to the knees. This disliking should not be underestimated after considering the importance to dress properly during salat. The Qur'an says: "O children of Adam! Adorn yourself at every time of worship" (7:31). It is worth to note that also some of the early Shia scholars have issued fatwas stating the 'awrah of a man being what is between the navel and the knees like Ibn Barraj in "al-Muhaddhab" and Abu al-Salah al-Halabi in "al-Kafi fil-Fiqh".
With prayers for your success.