Determining Whether Interrupts Are Enabled

Hardware Arduino Due
5 
/** \brief  Enable External Interrupt

    This function enables a device specific interrupt in the NVIC interrupt controller.
    The interrupt number cannot be a negative value.

    \param [in]      IRQn  Number of the external interrupt to enable
 */
static __INLINE void NVIC_EnableIRQ(IRQn_Type IRQn)
{
  NVIC->ISER[((uint32_t)(IRQn) >> 5)] = (1 << ((uint32_t)(IRQn) & 0x1F)); /* enable interrupt */
}

Looks like name of the register is ISER, and more from data sheet:

12.20.2
Interrupt Set-enable Registers
The ISER0-ISER1 register enables interrupts, and show which interrupts are enabled. See: