The 20-year-old has returned to England from Dutch Eredivisie bottom side Sparta Rotterdam.
Dobson's previous stay at Bescot was a season-long loan from West Ham in 2016-17, during which he played 26 times.
"We put a year of work into him and he was showing good promise and undoubted ability," said boss Jon Whitney.
"He really improved his fitness when he was here and we tried to get him on a permanent deal in the summer.
"I've kept in touch with George over the last four or five months and I'd like to thank the chairman and the board for providing additional funds to get him in."
Dobson added: "When Jon got in contact and said he was interested in taking me back, I threw myself at it.
"I loved my time at the club last year. I really felt like I kicked on as a player."