'Look at' is more often seall, occasionally seall air according to Faclair.com.
Mark shows usage with a variety of prepositions and with none:
seall, sealltainn v 1. eye, look, see □ seall thairis air overlook □ seall gu cùramach peruse □ seall cò th'againn! look who's here! □ sheall mi mun cuairt I looked around □ sheall e suas he looked up □ sheall e a-mach air an uinneig he looked out of the window □ sheall i a-steach air an uinneig she looked in through the window □ seall Seumas! look at James! □ seall a bheil briosgaidean teòclaid aca see if they have chocolate biscuits
seall is sometimes used with air / ri □ sheall e orm he looked at me / he eyed me □ sheall e ris a' chleoc he looked at the clock □ seallar ris a' cho-cheangal a tha eadar na dhà the connection between the two will be looked at □ seallar ri sin that will be looked at
Although neither says this explicitly, both sets of examples show that the usage is different. With a direct object it is used to mean 'look at suddenly', 'behold', often with a sense of surprise, as in this question or in Mark's example
seall Seumas! 'look at James!'
or Dwelly's rather patriotic example
Seall an gaisgeach treun a' teachd! 'see the conquering hero comes!'
whereas seall air is much more of a general 'look at to find out' - but still a one-off action not a continuous action. If you are going to look at something for a long time, like the TV, use coimhead air.
In real life, you can go by the gender of the noun for the thing being talked about. In the artificial context of these sentences without context they accept either. If you are talking about something where you are not sure what noun to use, or where you do not know the gender of the noun, you would normally use e but no one would criticise you if you used i.