When Oliver Cowdery copied from 𝓞 into 𝓟, he accidentally omitted the all in this sentence. In accord with the reading of 𝓞, the 1981 LDS edition restored the all. The use of “all thy thoughts” is undoubtedly correct since it is supported by similar instances of “all thy X” in the preceding text:
Summary: Maintain in Alma 37:36 the use of all in the phrase “all thy thoughts”, the reading of the original manuscript.