I've just checked my service schedule as my five year service was done last week. According to the handbook the brake fluid must be changed every two years but no mention of that happening in the book. The section in the latest service sheet about brake fluid OK or needs replacing is blank. Do I need to go to the garage or just ignore it? Car is Fabia VRS.

Get it changed ASAP, the moisture that will have built up in the fluid will corrode expensive parts (such as the ABS unit), as well as early brake fade. It's only £38 at most dealers, versus £xxx for new brake bits.

Can the garage test the fluid for water content ?

Yep they use something called a boil point tester - these are quite expensive to buy. TBH it's far easier to just change the fluid if there's any doubts, even if it probably was already replaced within two years.