I like that you want to satisfy your partner and thus seek to become informed - you must be a great lover! I am going to give you some known facts about female ejaculation but recommend that you invite your wife to guide you through her own genitals - women know and often feel to shy to tell partners.
At the outset it needs to be known that not many women can ejaculate, that in the world of sex research there remains controversy if this even exists. So go into this without expectations. Many women do not enjoy deep internal stimulation and many do. Who knows what your wife will enjoy.
Best time to stimulate her potential g zone area is when she is very aroused, swollen and lubricated. Seldom that she is likely to ejaculate before she is very aroused both in her body and her head and heart.
using your 2 fingers, palm up, make a "come hither" motion. In other words you are strongly stimulating the anterior wall of her vagina, 12 o' clock position. If she is very aroused, very relaxed and allows hersalf to have continuous stimulation, she may well ejaculate fluid from her vaginal area accompanied by a strong orgasm/s.
Buy a specifc g zone sex toy from my site: www.dreve.co.za and use it on her or try deep penetration with your penis. Women also report ejaculation just from clitoral stimulation.
Remember to have fun as you consensually explore.