Not able to get "Resolved" field from Jira Integration

Look at a definitely resolved Bug in Jira UI,  If you see a Resolved date there but it's not coming through the API, then it's likely an integration/permission issue rather than the field not existing.

Jira fields can be weird, but they're part of what adds the customizability to Jira.

If Jira has an official field that says "Resolved", it will show up in the API JSON as "Resolved". 

If your Jira Admin or project team added a custom field called "Resolved", it will show up as "customField123456" in the JSON. There is an API which gives the fields for a project, which should then tell you want custom field id you want.

On a past project, I solved some of these nuances by having Appian sync'ed records that were backed by an integration call to Jira's API's for project and issue type.

Someone who is familiar with Jira API setting can help you with this. Basically, the team managing JIRA Api should configure/confirm that Api will return the Resolved date in the response.
What a third party responds with when respective API is called , is not configurable from Appian rather response setup is done in third party system! 
If Jira API is setup to send resolved date then you will be getting it in Appian as well after a successful integration call!

I was able to get solution. "resolutiondate" should be the field name given in JQL query for Resolved field in JIRA UI.