How do you know if you have thyroid?

What do you mean: Everyone has a thyroid. Are you asking how do you know if your thyroid isn't working properly, either overactive or underactive? What symptoms are you having?

Thyroid: Most people do have a thyroid gland -- but it can develop problems of being either underactive (hypothyroid) or overactive (hyperthyroid). Hypothyroidism may result in sluggishness, weight gain, depression, hair loss, etc. Hyperthyroidism can cause anxiety/agitation, weight loss despite increased eating, bounding pulses, etc. Your doctor can feel your thyroid and also test its function.

Everyone has one!: Everyone has a thyroid. Otherwise, a person would not have thyroid hormone, and would be detected from the newborn screen done on a baby's blood prior to leaving the hospital after birth. If not detected then, the primary care doctor doing infant check-ups will detect the problem due to poor growth/development of the baby. Of course, a person with a thyroid removed by surgery won't have a thyroid.