“The days drew near for Israel to die.” Jacob was getting old, so the time when he would die was drawing near. Although some versions say, “must die,” that is not what the Hebrew text says. In the Hebrew text, “to die” is an infinitive.
“put your hand under my thigh.” This is a euphemism for “take hold of my genitals,” and it was done as part of the oath Jacob wanted Joseph to swear to him.
[For more on the practice of swearing an oath while holding the genitals, see commentary on Genesis 24:2.]