Here is a prayer composed by St. Gemma Galgani to obtain a desired grace:
Behold me at Your most holy feet, O dear Jesus, to manifest to you my gratitude for the continual favors which You have bestowed upon me, and still wish to bestow upon me. As many times as I have invoked You, O Jesus, You have made me content; I have often had recourse to You and You have always consoled me. How shall I express myself to You, dear Jesus? I thank you! Yet one more grace I desire of you, O my God, if it would be pleasing to You (here mention your request). If you were not omnipotent, I would not make this request. O Jesus, have pity on me. May your most holy will be done in all things"
-Prayer composed by St Gemma
Another prayer from Saint Gemma to Jesus:
O my crucified God, behold me at Your feet; do not cast me out, now that I appear before You as a sinner. I have offended You exceedingly in the past, my Jesus, but it shall be so no longer. Before You, O Lord, I place all my sins; I have now considered Your own sufferings and see how great is the worth of that Precious Blood that flows from Your veins. O my God, at this hour close Your eyes to my want of merit, and since You have been pleased to die for my sins, grant me forgiveness for them all, that I may no longer feel the burden of my sins, for this burden, dear Jesus, oppresses me beyond measure. Assist me, my Jesus, for I desire to become good whatsoever it may cost; take away, destroy, utterly root out all that You find in me contrary to Your holy will. At the same time, I pray to You Lord Jesus, to enlighten me that I may be able to walk in Your holy light.
--Prayer composed by St Gemma
Prayer to St Gemma asking for her intercession
Oh holy Gemma, I am near you, help me to pray. You who know what I and those near me need; look after my urgent needs and my spiritual and material wants. You take care of them! I confide in you and entrust all to your loving care.
Offer up to Jesus that tender and constant care that you bore Him here on earth.
Oh holy Gemma, you who physically suffered all the pains of the Passion of Jesus, I beseech of you the grace to meditate on and live the Passion of Jesus, and the sufferings of Holy Mary. Pray that I will be able to walk in the path of humility, simplicity, love and sacrifice, fulfilling at all times and in all ways, the holy will of God. Let me live united with Jesus, the Blessed Virgin Mary, and you, for all eternity. Amen.
(taken from a St Gemma Holy Card)
Prayer to St Gemma for purity -assistance against against temptations
Gemma's mother taught her from and early age to kneel on her hands and pray 3 Hail Mary's every day, asking the Blessed Mother to obtain for her the grace of purity. At the end of her life, nearing death, a companion went to check on her and found her kneeling on her hands, saying the 3 Hail Mary's for purity. Even at the end of her life she did not abandon this holy practice. Therefore, we can confidently invoke her for assistance against temptations of impurity.
Oh bright flower of heaven, St Gemma, mirror of purity and penance, obtain for us the grace of purity and help us against all temptations of the flesh. We ask this through Christ our Lord. Amen.
See also: Triduum in honor of St Gemma to obtain a special grace
and also Novena to St Gemma