To list all of the active jobs in the current shell, use the jobs command:

$ jobs
[1] + Running find / -name core -print >
trash
2>&1 &

Once you have listed the active jobs then you can bring them to the foreground using the fg command:

$ fg   %1
find / -name core -print > trash 2>&1    &

If you want to place a foreground job in the background then you need to suspend it with the ^Z (Control-z) command and then use the bg command:

find / -name core -print > trash 2>&1 &
^Z
[1] + Stopped (user)find / -name core -print > trash 2>&1 &
$ jobs
[1] + Stopped (user) find / -name core -print > trash 2>&1    &
$ bg   %1
[1]find / -name core -print > trash 2>&1 &
$