So, a visitor (whether they be from another planet or another reality) gets deposited on the face of the Earth. They find that the air's breathable, that water and suitable macronutrients are available, and that there are signs of sentient presence (us!) on this planet.
- Their inability to communicate fluently with the humans who they encounter
- And their inability to pass for a human under cursory examination
they are taken in to a research hospital for evaluation. What evaluations and tests would be performed on them?
We can assume that our visitor:
- Can't return home or bring more friends over
- Doesn't have an alien/otherworldly biology text/set of texts with them for us to study
- Is a carbon-based, aerobic, chemohetrotrophic life form -- their body can process Earth macronutrients (albeit perhaps with some difficulty), and does not need any micronutrients that cannot be obtained from Earth-food
- Is sentient, and has intelligence roughly comparable to an average human (within 2 sigma of the human average, certainly), as well as having vocal cords
- Has a bipedal (roughly humanoid) body plan, with plantigrade locomotion and opposable thumbs
- Does not have to concern themselves with human diseases, and cannot transmit any diseases of alien origin to us
- Is in good physical condition, with no serious heritable disorders
- Is docile and understanding regarding our obvious curiosity, and wants to understand us in return -- obviously, they'd rather be alive than dead, though, and probably would react badly to us trying to kill them.
- May have subtly different biochemistry to us -- not enough to make Earth uninhabitable long-term, but the possibility exists that, say, blood tests may return odd results.