Also back for Magners League action is fit-again centre Gavin Evans as teammate Rob Higgitt starts on the bench.
Jones captains the team in place of Simon Easterby who is recovering from knee surgery.
Davies said: "We can expect a huge challenge at the RDS. Leinster had a fabulous victory last weekend in the Heineken Cup semi-final against Munster.
"It was a smashing game of rugby and they were very impressive indeed. The have a strong forward platform this season which, perhaps, they've struggled with in years gone by and they can front up in that area.
"They've always had the quality backs who can damage teams. They have a lot of experience and they've benefited from a consistency of selection this season."
Tomorrow's game is the first of three the Scarlets play in eight days to end their league campaign.
Davies said: "It's a bit bizarre. We started the season with three games in a week and end it the same way - it means that, effectively, a third of our season is sorted out within two weeks.
"It's not ideal but everybody's got to face it and deal with it, particularly the teams that have progressed in Europe and in the Anglo-Welsh cup competition.
"It's got to be looked at because six games in two weeks isn't what anybody really wants.
"However, we've focused well this week and our aim is to go and win our final three games."
Scarlets team
Leinster (a), Fri 8 May, 7.45pm, RDS, Magners League
15 Daniel Evans, 14 Mark Jones, 13 Gavin Evans, 12 Jon Davies, 11 Lee Williams, 10 Stephen Jones (c), 9 Martin Roberts, 1 Iestyn Thomas, 2 Matthew Rees, 3 Phil John, 4 Vernon Cooper, 5 Dominic Day, 6 Josh Turnbull, 7 Johnathan Edwards, 8 David Lyons. Replacements - 16 Deacon Manu, 17 Ken Owens, 18 Lou Reed, 19 Rob McCusker, 20 Gavin Cattle, 21 Rhys Priestland, 22 Rob Higgitt.
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