One who is unsure as to the correct blessing:[1]

If even after one’s study and research he is still left in doubt in regards to which blessing is to be recited over the product, either due to a Halachic question or dispute[2], or due to not knowing at all what the food item is [and cannot tell if it is a fruit, or vegetable, or a Shehakol product], then one is to recite the blessing of Shehakol, being that it covers all products. [Alternatively, one is to eat the product within a meal of bread, if it is a food that can be exempt with Hamotzi. This indeed is the better option, as in such a case there’s no doubt at all regarding the blessing.[3]]

Lechatchila:[4] The above law is only Bedieved, however initially it is forbidden for one to fulfill his obligation with the blessing of Shehakol and rather one must research and study what blessing is to be said for the corresponding food and if one is not knowledgeable in the laws of blessings then he is required to study the laws with a Rabbi as explained in Halacha 14.

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[1] Seder 1:4-5; Luach 1:5; Admur 204:24; Michaber 204:13; Rama 202:18; M”A 202:36; Tur 202; Rosh 6:6; Rabbeinu Yona Brachos 25a

[2] Such as rice [Seder 1:10] or fruit soup [Seder 7:12] or a fruit which has completely disintegrated [Seder 7:22-24], or soup from vegetables that have cooked in vinegar [Seder 7:21] or legume porridge that has been slightly cooked [Seder 7:24]

[3] Admur 204:24; Omitted from Seder and Luach ibid, despite Admur bringing this concept regarding rice in Seder 1:11!

[4] Admur Seder 1:5; Luach 1:5; Admur 202:24; M”A 202:36; Rabbeinu Yona Brachos 25a; Ketzos Hashulchan 49:3