{
  "@context": [
  	"http://nonexisting.example.com/context",
  	{ "ex2": "http://example.com/2/" }
  ],
  "@id": "ex2:a",
  "ex:term2": "ex2:b"
}

Test with term2, not ex:term2 (to get @type:@id)
{
  "@context": [
  	"http://nonexisting.example.com/context",
  	{ "ex2": "http://example.com/2/" }
  ],
  "@id": "ex2:a",
  "term2": "ex2:b"
}