If it fails, it'll tell you. You can also check the exit code '$?'; should be 0 (zero) for success.
If this is in a script, make sure you check the exit code and log both stdout and stderr eg
# call script
./myscript.sh >myscript.log 2>&1
# basic code for script
scp myfile user@host:/dir/myfile
if [[ $? -ne 0 ]]
echo "scp failed with $?"
The error msgs will appear in the logfile.