If you have a non-magical “Sense Magic” ability, e.g. the Chuul’s, but you are inside an antimagic field, can you detect magic (from a source that is outside the field)? The ability states:
The chuul senses magic within 120 feet of it at will. This trait otherwise works like the detect magic spell but isn’t itself magical.
So that means that this trait would not be nullified by an antimagic field.
Detect magic itself has 2 parts, first “sensing the magic”, and secondly seeing it’s aura:
For the Duration, you sense the presence of magic within 30 feet of you. If you sense magic in this way, you can use your action to see a faint aura around any visible creature or object in the area that bears magic, and you learn its school of magic, if any.
The spell can penetrate most barriers, but is blocked by 1 foot of stone, 1 inch of Common metal, a thin sheet of lead, or 3 feet of wood or dirt.
Now, Antimagic Field (the spell) states that:
This area is divorced from the magical energy that suffuses the multiverse. Within the Sphere, Spells can’t be cast, summoned creatures disappear, and even Magic Items become mundane.
Spells and other magical effects, except those created by an artifact or a deity, are suppressed in the Sphere and can’t protrude into it.
So would the magical auras, which Detect Magic allows you to see, even be able to reach you while you are within the field? I couldn’t really find a RAW or RAI definition of whether these auras count as a “magical effect”, or if they are, essentially, just a non-magical energy emission that you can’t normally see, and detect magic simply expands you visual range to encompass it.
And the first part, that of sensing the magic in the first place, is left completely up to our imagination, but there most likely must again be some kind of emanation that has to reach your player, so the same question arises.