You can kinda tell by feeling your hair while its wet. If it feels softer and kinda gummy that's a sign. Also, check a strand of shed hair, pull it and if it stretches a good deal more than you think it should that's another sign. If your curls are looking rather limp and lifeless no matter how much you've clarified then that's a sign. All these are signs your hair might be lacking in protein. Shedding, breaking, and thinning more than usual can also be indications.

If your hair needs moisture if it won't stretch, doesn't feel soft, is breaking, and dull.

If you're not sure you can always do a simple protein treatment and see how your hair reacts to it, like Joico KPak or the reconstructing treatment by Ion.
Thick coarse 3c/4a prone to dryness.
Staples
Aphogee 2 Step treatment
Generic Biolage Conditioning Balm
Tigi MM Conditioner
Creme of Nature Shampoo for dry hair
KCCC
Denman D3
Giovanni Direct Leave-in
SheaMoisture Leave-in
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"Make it work!"- Tim Gunn