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Hearing the Blessing from another person: 
If the other is also putting on a Tallis: If many people are putting on a Tallis at the same time, each person is to say the blessing on his own. Alternatively, they can choose to have one person say the blessing, and the remainder will listen and answer Amen. [Bedieved, a listener fulfills the blessing even if he did not answer Amen.]
If the other person is not putting on a Tallis: One who is not putting on a Tallis at the moment cannot say a blessing on behalf of another person that is putting on a Tallis, if that person knows how to say the blessing himself. If however the person does not know how to say the blessing then another person may say the blessing for him.
What is the definition of not knowing how to recite the blessings?
Seemingly this means the person has difficulty verbalizing the Hebrew words, or does not know the dialect of the blessing. There is no obligation for someone to read him the blessing and have him repeat the blessing after him. However, some Poskim write it is best to do so, although the person is not to say Hashem’s name.
 8/11; Michaber 8/5
 So writes Admur ibid; Michaber ibid writes “two or three”; See 489/1 that Admur writes that one is to have ten people to be Yotzei the blessing of Sefira with another. Vetzaruch Iyun!
 Through doing so they fulfill their obligation being that one who hears is considered like one who has spoken. [Admur ibid]
May one be Yotzei the blessing from another person even if a Minyan is not present? Yes [Admur 59/4; Michaber ibid; implication of Admur ibid; See however 489/1 in previous footnote, Vetzaruch Iyun.]
 Admur 213/4; Michaber 213/2; Kaf Hachaim 8/24
 Admur ibid and in 585/5; 273/6; M”A 8/8; 585/3 based on Terumas Hadeshen 140; P”M 8 A”A 8; Opinion in M”B 585/5 and 692/10; Kaf Hachaim 8/21
Other opinions: Some Poskim rule the person may always say a blessing for the other even if he knows how to recite the blessing. [Rama 585/2 regarding Shofar; Elya Raba brought in Kaf Hachaim ibid ]
 The reason: Although he is doing so in order to exempt that person and have him fulfill his obligation, nevertheless he cannot say the blessing being that he himself does not need to now say the blessing. [ibid]
 The reason: Although the person who is saying the blessing is not fulfilling the Mitzvah at the moment, and hence does not need the blessing, nevertheless since all the Jewish people are guarantors to each other, therefore it ends up that he too needs this blessing now [due to his obligation of a guarantor]. (It is for this reason that it is accustomed for the Chazan to recite the blessing [over Tzitzis] aloud in order to fulfill the obligation of one who is not an expert.) This same law applies by the blessings of all Mitzvos. [ibid] See P”M 8 A”A 8; Kaf Hachaim ibid
 So is implied from M”A 585/3; See Background.
 Pashut as otherwise all the above Poskim would have simply stated for this to be done; Furthermore, perhaps from the fact that the Poskim do not mention this option one can derive that it is forbidden to do so, being that at least one person is saying a Bracha Levatala when one says it after the other word for word. See Admur 215/2 “Although it is forbidden for a Gadol to be taught [the blessings].” However, seemingly there it only refers when the Gadol does not currently need to say the blessing, however when he needs to say the blessing then perhaps it is permitted to teach him, and have him repeat word for word. [so is implied from explanation of Rebbe in Igros Kodesh 3/138] Furthermore, the Tur in name of the Rosh explicitly rules that by Birchas Hamazon one may recite the blessing word after word for the other. Although perhaps Birchas Hamazon is an exception, Vetzaruch Iyun!
 Kaf Hachaim 8/21