$ sudo ls -la /var/lib/cloud/instance/scripts
total 12
drwxr-xr-x 2 root root 4096 Feb  6 02:25 .
drwxr-xr-x 5 root root 4096 Feb  6 02:38 ..
-rwx------ 1 root root 1278 Feb  6 02:38 part-001

If you open part-01, you can see your EC2 Instance UserData scripts

$ sudo cat /var/lib/cloud/instance/scripts/part-001
#!/bin/sh -xe
yum update -y

function error_exit{
  /opt/aws/bin/cfn-signal -e 1 -r $1 https://cloudformation-waitcondition-us-west-2.s3-us-west-2.amazonaws.com/XXXXXXXXXXXXXXXXXXX
  exit 1
}
yum install -y aws-cfn-bootstrap
/opt/aws/bin/cfn-init -v --stack a999 --resource EC2 --configsets default --region us-west-2 #  || error_exit 'Failed to run cfn-init'
/opt/aws/bin/cfn-signal -e $? -r $1 https://cloudformation-waitcondition-us-west-2.s3-us-west-2.amazonaws.com/XXXXXXXXXXXXXXXXXXX

And it can run by manually

$ sudo /var/lib/cloud/instance/scripts/part-001