Jsonapi query to return specific field
Yes, with the caveat it still contains the JSONAPI document payload around your requested field. This is mandated by the spec so you can't just have an arbitrary JSON structure that contains only the field data you want.

This is called a sparse fields query. When you add a ?fields[$RESOURCE_ENTITY]=field1,field2... to a:


index endpoint (/jsonapi/node/article)
resource endpoint (/jsonapi/node/article/$UUID) endpoint


It will trim down the list of fields to the comma-delimited list you've specified.

To use your example, http://localhost:8080/jsonapi/node/article?fields[node--article]=body will return a JSONAPI document with all article nodes with only the body property in the attributes object. 

See the JSONAPI docs about fetching resources for more info.