Can anyone suggest whether there is any possibility how to trigger a SP2013 WorkFlow using REST API & Jquery ?
Yes there is, see for a detail example Start workflow using rest call
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I would suggest the best way would be to have a workflow that waits for a field to = x then you use the api to update an item and set the field to x.
I have shared how you could start a workflow in sharepoint online on office 365 by calling the REST API at _vti_bin/client.svc/ProcessQuery, basically you will need to do HTTP Post at the end point twice, one to get the workflow subscription and the other to trigger the workflow instance to start, find it here https://community.nintex.com/community/tech-blog/blog/2017/01/18/stronger-together-nintex-workflow-cloud-office-365
No, there are no coverage for workflow or taxonomy in SP REST API.