Dev and Beigh (65 batting) responded to Assam's first innings total of 263 all out with a solid batting display as the hosts extended their lead to 31 runs with five wickets remaining at the end of day two.
While Dev's unconquered 192-ball knock was laced with six fours and two sixes, Beigh's unbeaten 152-ball 65 had eight hits to the fence.
Jammu and Kashmir started off strongly in their reply as the pair of Adil Rishi (34) and Obaid Haroon (32) put on 69 runs for the opening wicket.
For Assam, Arup Das and Pritam Das accounted for two wickets apiece.
Brief Scores: Assam: 263 all out in 87.5 overs
Jammu and Kashnmir: 294 for 5 in 87 overs (Ian Dev Singh 94 batting, Samiullah Beigh 65 batting; Arup Das 2/61).