who suggested the title The Wasteland to T.S Eliot?
No one particularly. The poem was written at a time of turmoil, in the aftermath of World War I, and its fragmented structure is reflective of the terrible sense of disorder that Eliot and his contemporaries must have experienced. T.S. Eliot named Jessie L. Weston's book: Ritual to Romance (1920) as the source for the title, structure and some of the symbolism of his poem. Yet, it is difficult to weigh the extent of the influence of Weston's analysis of the myth of the Holy Grail on The Wasteland, for Ritual to Romance was published several months after Eliot had made it known that he had been working on The Wasteland (The original title of the poem was He Do the Police in Different Voices.). Weston in her book took a historical approach and described the development of some of the fertility rites of ancient Greece and the Near East into the medieval tales of the quest for the Holy Grail. Eliot in The Wasteland tried to work backwards, reaching out to their religious sources from within the legends themselves. In her study, Jessie L. Weston placed a special focus on the motif of the Waste Land the fruitfulness of which could have been restored by the finding of the Holy Grail. It is not difficult to imagine that what Eliot tried to accomplish through his poem was to locate a source that may have contributed to the rejuvenation of the degenerate society and culture of his time. This may be an explanation for his eventual choice of Wasteland as the title of his poem.
You can read Jessie L. Weston's book online: