Hello, some years ago I read a novel trilogy about Trajan's life and in the last book it shows the bad relationship Trajan had with Hadrian, and how Trajan was planning to designate as succesor an african general from his legions instaed of Hadrian. It the last scene, Trajan is going back to Rome in a ship (in theory to stop Hadrian from fucking up Judea) and its poisoned during the trip, it is also revealed that it was his Wife and Hadrian that planned his death.
How historically accurate is this?
To answer your question concisely, no. There's no evidence for this and no reason to believe this is what occurred. While there's some theories to suggest that Trajan had reservations about naming Hadrian his heir, their relationship was in no way "bad" at the time of Trajan's death. Hadrian was at the time governing the province of Syria on Trajan's appointment, a very prestigious post (not to mention his marriage to Trajan's grandniece), making him, essentially, heir-apperant. Many sources claim that Trajan was considering naming Lucius Neratius Priscus as his heir, but Hadrian was clearly in the running and held significant favor with Trajan. It's true that Hadrian was very close to the empress Pompeia Plotina, and she openly desired him as heir. On Trajan's death, a document was produced by Plotina naming Hadrian as Trajan's choice, but many believe she forged his signature. Of all the rumors that circulated at the time, none indicated any foul play regarding the death itself. The most scandalous rumor circulating at the time was that Plotina hired an actor to impersonate Trajan after his death and name Hadrian heir, but this comes from only one source (Cassius Dio, having heard this from his father) and is very unlikely for obvious reasons. Trajan was in his mid-sixties when he died, and had been ill for several months leading up to his death. In fact, his return to Italy was because of his sickness, he did not fall ill on the way. As far as Judea, the Second Roman-Jewish War (and subsequently, Hadrian's intervention in Judea) would not begin until 132, fifteen years after Trajan's death.
Sources:
Francesca Santoro L'Hoir, Tragedy, Rhetoric, and the Historiography of Tacitus' Annales. University of Michigan Press, 2006, ISBN 0-472-11519-7, p. 263
Birley, Anthony R. (2013). Hadrian: The Restless Emperor. Abingdon: Routledge. ISBN 978-0-415-16544-0.
Benario, Herbert W. (2000). "Trajan (A.D. 98–117)". De Imperatoribus Romanis. Retrieved 24 September 2007.