Consider the following, fill in for YOUR-HOST and YOUR-SITE for your checkmk monitor and TARGET-HOST for the host whose CPU utilization you want. You’ll need to supply an Authorization header with “Bearer YOUR-AUTOMATION-USER YOUR-AUTOMATION-PASSWORD”:
https://YOUR-HOST/YOUR-SITE/check_mk/api/1.0/domain-types/service/collections/all?query={"op": "and", "expr":[{"op": "=", "left": "host_name", "right": "TARGET-HOST"}, {"op": "=", "left": "description", "right": "CPU utilization"}]}&columns=host_name&columns=plugin_output