200 Amp Service upgrade Failed Inspection NJ
Heres my guess.  It's an easy one indeed.   By "multi wire circuit" he actually means multi-wire branch circuit.  This is a special method of running 120V circuits where you get 2 circuits' worth of power on one /3 cable, by sharing neutral.   You can google it, but the highlights inspectionwise are 


the circuit must have neutral pigtailed, you can't use a receptacle etc. as a splice point for the onward neutral or you'd knock out both sides of the circuit if you removed the device.  
Both legs must, must, must be on opposite poles.
both legs of the MWBC must have common maintenance shut-off, so the usual technique of "turn breakers off until the radio stops playing" turns off the whole circuit.  


That last one is what you are being written up for.  

In a residential breaker panel (as opposed to fuses or industrial), you do that one of two ways.   You use a 2-pole breaker  (like you would for a water heater, but the correct amperage)... Or you use listed "handle ties" that are correct for that breaker type. These are weird and specialty, and big-box rarely carries them.  Sourcing them is such a hassle that I just advise people to use 2-pole breakers, which are sold everywhere for $10. This also leads them into correct decision making when selecting AFCI or GFCI breakers later. 

Where

So you need to search your panel for circuits which have 3 conductors, not including ground: two hots and a neutral.  In a panel like yours with all cables, the dead giveaway is a red wire for the second hot. 

Follow each of them, and make sure every one lands on a 2-pole breaker.   If you find a pair going to two singles, measure the voltage at the breaker between the two "hots".  It had better be 240V.  If it's not, congrats, you just dodged a house fire.   Move those two "hots" to a 2-pole breaker of same amp rating.   

The reason I advise 2-pole breakers in your case (besides the annoyance of finding listed handle ties) is that way, you don't even need to chase it to figure out if it's an MWBC.  2-pole breaker, done...