Daniel Jackson: Hobbies
One pastime he does indulge in is keeping a personal journal for each of the missions undertaken by the SG-1 team. When Sam Carter read out a page from an early journal when Daniel was believed by the team to be dead (1.13 "Fire And Water"), it was clear he began this tradition during the first mission to Abydos. Daniel's private journals are handwritten and contain both archaeological and personal observations, some, naturally, about Jack O'Neill.
He rarely takes time off from the job, often working around the clock. What little social time we have observed him spending during the course of the series has been with other members of his team. When Sam Carter was ordered to rest and recuperate from suspected exhaustion, Daniel was the one to empathise and commiserate with her on being forced to take it easy (5.03 "Ascension"). Taking it easy is not something either Daniel or Sam find easy.
In common with all the members of SG-1, Daniel plays chess. Even when debilitated by Ma'chello's Goa'uld killing technology (3.04 "Legacy"), he was capable of easily defeating Jack. When trapped on base after being compromised by the sentient alien computer program Urgo, Daniel and Teal'c chose to while away the hours playing chess.
Recently, Daniel has been observed spending time working out in the gym with Sam (7.04 "Orpheus") and Teal'c (7.15 "Chimera"). His physique has certainly changed since his early days on the team, paralleling his evolution into a more active participant into the military aspects of the missions.
A recent revelation is that Daniel is a pretty good basketball player. He went two-on-two with Cameron, Teal'c, and Vala, and has played with Cameron on other occasions (9.06 "Beachhead", 9.10 "The Fourth Horseman Part 1").
Sam and Daniel have discussed movies - she made a point of bringing him up to speed on all the movies he'd missed while ascended (7.04 "Orpheus") but it has never been established if Daniel even owns a television set. Or a music system. He did own a piano (4.18 "The Light") which we've never seen him play.
Daniel does love to read. In fact, he loves it so much, when the Atanik armbands upgraded him, Jack and Sam to superhumans (4.03 "Upgrades"), he was bouncing with glee because, as he endearingly confided to Tok'ra scientist Anise, he could "read really fast!"