Cockbain has been out for seven months after suffering a detached hamstring in Wales' autumn international victory over Fiji.
Jones has barely played since starring on last summer's British & Irish Lions tour after undergoing shoulder reconstruction surgery.
The loose forward said: "This is going to be a massive year for the Ospreys and also for Wales, with the World Cup.
"I am taking nothing for granted and will be grateful just to get back on the field, but it is brilliant to be a part of things again."
Jones and Cockbain have been joined at pre-season training by Ospreys team-mate David Bishop, the centre who has recovered from a fractured knee cap.
Ospreys conditioning coach Huw Bevan said: "We have got really back into the swing of things this week after the holiday break and it is great to have Ryan, Brent and Bish back with the squad.
"The boys have just started a concentrated conditioning period and the guys returning from their long-term injuries will take a full part in the programme.
"We do not start our rugby phase for a few weeks but it is great to have these guys back on board."