Como dizer "Reconhecer o (sentimento de saudade)'' em inglês

Well, to answer this one it could be necessary to dig deeper and get a fuller picture. But here you go, a kick-off then:
He/she could have Aleximya - He/she has inability/great difficulty to identify and describe their own emotions and that of others. Emotions simple go under their radar.

Other possibility is the subject/person doesn´t allow themselves the feelings that come to them. They just try to numb or avoid them. They "bottles these feeling up" (guardam para si/os reprimem) and that ends up coming back with a vengeance, or robbing the person of some necessary experiences or appreciating some good ones.

And perhaps you want some more simple description: "he is incapable of feeling any emotions, including the longing for someone else."
It´s worth noticing, that "being incapable of showing any emotions" may be mistaken for or confused with "being incapable of feeling any emotion", a common mistake.