Inclusive of what eltrouble said you want to try and knock Sim down or push him back as soon as the round starts. You can use cr.forward to knock him down cleanly when he attacks with slides, cr.strong/fierce, or st.fierce. You only want to go for the crossup when you have a close-range knockdown because Dhalsim can escape AND punish if you jump from a bad range. If you’re unable to get close-range knockdowns, use the forward or roundhouse dread kicks to push Dhalsim into the corner, and then pressure him with cr.roundhouse, st.short (good vs. slides), and cr.strong (against his slides or db.forward/strong).
Here are a couple points to remember:
vs. Yoga Fire outside of DJ’s cr.roundhouse range – You can either trade by using short dread kick, do a kara-short upkick (charge down 2 sec, cr.roundhouse – up + short), or attempt to walk a bit and hit Sim’s head with st.fierce or st.roundhouse which is very risky. Also, if the Dhalsim likes to do close-range db.forward/roundhouse into yoga fire, you can always short or forward up kick (or super) before the yoga fire reaches you.
vs. Noogie Traps – Machine gun upper if you have the charge; otherwise, you can try to counter throw since most Dhalsims attempt to noogie within DJ’s throw range. Forward and roundhouse dread kicks will work as well, but it is entirely dependent on the Sim’s timing; you can be grabbed out of them if he does the noogie late. Finally, any up kick or super will beat the throw attempt but you better be sure about it and have the charge after mashing against the initial noogie.
vs. Drills – St.strong will beat any drill at any range as long as you time it properly. Any version of the up kicks will suffice as well.
vs. Jumping Normals – St.fierce will beat Dhalsim’s air normals as long as you are in front of them. If you’re under them you’re likely in range to punish whether or not they hit, but in the case that you aren’t within punish range you’ll want to use st.strong a little bit ahead of time to guarantee a clean hit.
vs. Yoga Flame – You can hit Dhalsim’s yoga flame with either a short dread kick or well-timed max out. The short dread kick must be done slightly in advance of the yoga flame, and the max out must be sent just before the flame dissipates. A super doesn’t have to worry about any of that though :D.
vs. Dhalsim on Wakeup – DJ’s crossup is more effective on Dhalsim than any other character. Take advantage of this by aiming either at the back of his head (non-crossup) or the back of his neck (crossup). You should be hit-confirming cr.jabx2 into machine gun upper, cr.jabx2, st.strong – roundhouse dread kicks, or cr.jab, cr.fierce into machine gun upper or up kicks (with super available). If he blocks the crossup, you’ll want to use jabx2 as a low (cr.forward)/throw mixup, or you can use a block string into forward/roundhouse dread kicks if you need to put Dhalsim in a certain area of the screen.
Let me know if this helped!