Can anyone tell me how to figure out what key I sing in?
Sure: write down the notes you are singing. Check which major or minor scale comes closest to it. That should work for most tracks.
Can anyone tell me how to figure out what key I sing in?
It really depends on the pitch range of any particular song. Some songs you'll sing comfortably in C, others might be in E. It just depends on how well the song's pitch range fits within your vocal range.
You should know what is your best key for each song that you intend to play and sing. Find your vocal limits (lowest and highest) and make sure any song you sing, doesn't exceed those limits - whatever key it's in.
You can sing in every key, as Fretsource said it's the pitch range of the song.
Tim Madsen
Nobody cares how much you know,
until they know how much you care.
"What you keep to yourself you lose, what you give away you keep forever." -Axel Munthe
Totally 100% correct.
What Fretsource and Tim_Madsen said.