I work in behavioral therapy and the best advice I can give you is to shape that behavior into something you find more appropriate. If what you think he’s seeking is oral sensory input then handing him a teether or some other “chewy” when you catch him biting his nails and saying “you can bite this instead” would work. Over time you’d want to fade your prompting and it could look like “oh I see you’re biting your nails, what can we bite instead?” And guide him to his teether. Have it accessible to him during times you notice he tends to bite his nails (or all day, if necessary). He’ll be more likely to use it as a replacement if it’s always within reach. If you think it’s not oral sensory input he needs but tactile instead try offering him textured things he can run his nails on (textured books, flashcards, a sensory bin, kinetic sand, water play might work too). And same thing, over time, fade your prompts and make sure the replacement tool you’re using is available. Eventually the goal is he goes to get it on his own when he needs that sensory input. But the replacement just depends on what he’s getting out of biting his nails and what you feel is appropriate and works for your lifestyle. We all have a need for sensory input and we use it as a calming/coping skill…some people twirl their hair, or shake their foot while they sit. So we want to acknowledge he’s probably using this to regulate but just give him something more appropriate. Hope that helps!
Re: 29 month old boring finger nails