The back ticks are at wrong place. The index must be as follows.
As there is no special characters in the fields you can omit back ticks also.
CREATE INDEX `type-id-index` ON
`dev_hostel`(data.type,data.id);
FYI: _host is object and kind is field(nested) in object.
You reference as _host.kind or `_host`.`kind`. If you do `_host.kind` it looking field "_host.kind" not sub object.
If you want reference s1 you must use `f1.f2`.s1 because there is dot in the field you must do `f1.f2`.s1
{
"_host": {
"kind": "KIND1",
"id": "ID1"
},
"f1.f2": { "s1": 10}
}