What this dual-diode is and where it goes
A 40 ns trr at 30 A reduces reverse-recovery charge, lowering switching loss and ringing in hard-switched converters. The 1.75 V forward drop at 30 A is a trade-off for the speed.
Common-cathode pair — board-level fit
The common-cathode configuration shares the centre pin (cathode) between both diodes, so the TO-247-3 package gives you two independent anodes on the outer pins. That matches the topology of a centre-tapped secondary winding or a two-switch forward converter where the cathodes tie to the output rail. The through-hole TO-247 body is large enough to bolt to a heatsink with a screw — plan for a thermal pad or insulator if the heatsink is grounded.
STMicroelectronics lists the STTH60AC06CW as an active product.