Question about BenQ Gl2760h

Use the white cable.

If you have a 27" iMac, then yes... if only 21.5, then also, but would not fit from the size...
But I wouldn't take the monitor... because your iMac, if 27", has a resolution of 2560x1440... but this monitor from benq only 1920x1080... that looks pretty stupid side by side...

Your iMac has minidisplay port... so you need an adapter
For VGA:
Apple Mini DisplayPort to (VGA, 20cm)

for dvi:
Apple Mini DisplayPort to (DVI, 20cm)

for hdmi:
Bandridge SM Mini DisplayPort to (HDMI, 20cm)

So if the monitor you buy has only vga, then you take the vga adapter with a vga cable.... --> not recommended...
best is hdmi
there is even a mini displayport to hdmi cable:
Maxxtro Mini DisplayPort to HDMI Cable (1.80m, White)

So I wouldn't take this monitor:
if you have a 27" imac, i recommend this monitor:
AOC Q2778VQE (27", 2560x1440)

If you have a 21.5" imac then this one:
BenQ GL2250HM (21.50", 1920x1080)

and then you would need to buy the mini displayport to hdmi cable linked above.

I hope I was able to help.

Greetings