Can a RDF statement have more than one subject?

Question

If your answer to this question is yes, could you give me an example using the JSON-LD format?

Answer 1

The answer is no.

From RDF 1.1 Concepts and Abstract Syntax:

1.2 Resources and Statements

Asserting an RDF triple says that some relationship, indicated by the predicate, holds between the resources denoted by the subject and object. This statement corresponding to an RDF triple is known as an RDF statement. The predicate itself is an IRI and denotes a property, that is, a resource that can be thought of as a binary relation. (Relations that involve more than two entities can only be indirectly expressed in RDF.)

---

If you are just looking for syntactic sugar for multiple statements with common terms. —

In Turtle, there are predicate lists and object lists, however, there are no subject lists.
See also this question: List in front of the expression in OWL.

Update

In JSON-LD 1.1, you can use the @reverse keyword, i. e. write something like

{
  "@id": "#homer",
  "http://example.com/vocab#name": "Homer",
  "@reverse": {
    "http://example.com/vocab#parent": [
      {
        "@id": "#bart",
        "http://example.com/vocab#name": "Bart"
      }, {
        "@id": "#lisa",
        "http://example.com/vocab#name": "Lisa"
      }
    ]
  }
}

instead of

[
  {
    "@id": "#homer",
    "http://example.com/vocab#name": "Homer"
  }, {
    "@id": "#bart",
    "http://example.com/vocab#name": "Bart",
    "http://example.com/vocab#parent": { "@id": "#homer" }
  }, {
    "@id": "#lisa",
    "http://example.com/vocab#name": "Lisa",
    "http://example.com/vocab#parent": { "@id": "#homer" }
  }
]

Answer 2

Actually, the answer may need some clarification. An RDF statement cannot have more than one subject because it does not have any subject, in the sense of "subject" defined by the RDF specification.

It is quite common to talk about "RDF statement" when one wants to talk about "RDF triple" instead. An RDF triple is a syntactic construct that is a sequence of three elements that are called, in order, subject, predicate, and object. There is exactly one subject per RDF triple. A subject, in the sense of the RDF specification, is either an IRI or a blank node. An RDF statement, however, is not an RDF triple. It is the fact that an RDF triple is expressing. For instance, if I say that the Earth revolves around the Sun, I'm making a statement. The Earth is not a subject in the sense of the RDF specification because it is not an IRI (a sequence of character that follows an RFC specification) or blank node (an existential variable). It is a planet made of stuff, none of which are UNICODE characters, of course. However, I can write an RDF triple that expresses the statement:

dbr:Earth  onto:revolvesAround  dbr:Sun .

dbr: being the prefix for DBpedia resources https://dbpedia.org/resource/. This expresses the RDF statement according to which something (denoted by dbr:Earth) is related to some other thing (denoted by dbr:Sun) according to a relationship denoted by onto:revolvesAround. But this statement could equally be expressed using the following triple:

wd:Q2  onto:revolvesAround  wd:Q525 .

wd: being the prefix for wikidata https://www.wikidata.org/wiki/. The statement is the same (considering that it is stated in DBpedia that dbr:Earth owl:sameAs wd:Q2 and dbr:Sun owl:sameAs wd:525) but the triples are different. In particular, the subjects are different. So, in a certain sense, you could argue that there can be multiple subjects for the same RDF statement. Whether you represent it in JSON-LD or anything else does not really matter.