It is currently not possible to view via the API the user who approved a manual approval step. This user should be listed when requesting the data for the job that required approval API currently lists:
"committer_name" : "Allen Rohner", "committer_email" : "",
A similar convention for approval could be used, and to indicate if a job is an approval job. Example:
approval: { "approval" : true "approver_name" : "Allen Rohner", "approver_email" : "", }