Which cable should I use?
If my Imac has the thunderbolt logo On the port and the macbookpro has the mini dp logo which cable should i use ? Currently using mini dp cable and not working (mac book pro 13 mid 2013 with Imac 21.5 late 2103)
You need a Thunderbolt to Thunderbolt cable. Use your iMac as a display with Target Display Mode - Apple Support
Both computers as you list them have Thunderbolt connections. All Macbook Pros since 2011 have Thunderbolt.