You need to use below command for the same
docker stack ps --no-trunc
You can also find this in the command help by running the --help flag:
$ docker stack ps --help
Usage: docker stack ps [OPTIONS] STACK
List the tasks in the stack
Options:
-f, --filter filter Filter output based on conditions provided
--format string Pretty-print tasks using a Go template
--no-resolve Do not map IDs to Names
--no-trunc Do not truncate output
-q, --quiet Only display task IDs