The easiest way to find the key signature of a song is to look at the symbol at the song’s beginning. This symbol will tell you which notes will be sharp or flat for the rest of the song.
Another way to find the key signature of a song is to look at the first and last notes of the song. If the first and last notes are the same, the key signature is likely to be in that key. For example, if the first and last notes are both C, then the key signature is likely to be in the key of C.
If you’re still unsure, you can always ask a music teacher or another musician. They will be able to help you figure out the key signature of a song.