He travels for the purpose of study and comes back at the weekend; can he shorten his prayers?
Question

                I travel from my city to another city to attend a training program as part of completing my studies. This training lasts for six months, five days a week, after which I come back to my city to spend the weekend there. I have been shortening my prayers for the last two months; should I continue to shorten my prayers for the remainder of the period?
Praise be to Allah.If the distance between your city and the city to which you are travelling is 80 km or more, then you may shorten your prayers during your journey there and your journey back again.
When you reach the city, if you intend to stay there for more than four days, then you must offer your prayers in full from the moment you reach the city, according to the majority of scholars.
Ibn Qudaamah (may Allah have mercy on him) said:  If the traveller intends to stay in a city for more than twenty-one prayers, he should offer the prayers in full. The well-known view narrated from Ahmad (may Allah have mercy on him) is that the period of intended stay which requires the traveller to offer his prayers in full is that which is longer than twenty-one prayers. This was narrated by al-Athram, al-Mirwadhi and others. It was also narrated from him (i.e., Imam Ahmad) that if the traveller intends to stay for four days, he should offer the prayers in full, and if he intends to stay for less than that, he may shorten his prayers. This is the view of Maalik, ash-Shaafa‘i and Abu Thawr.
End quote from al-Mughni (2/65).
It says in Fataawa al-Lajnah ad-Daa’imah (8/99):
The journey in which the concessions of travel are prescribed is whatever is regarded as travel according to custom, and the distance is approximately 80 km. So whoever travels this distance or more may avail himself of the concessions of travel, namely wiping over the khuffayn (or socks) for three days and nights, putting prayers together and shortening them, and not fasting in Ramadan. If the traveller intends to stay in a city for more than four days, then he may not avail himself of the concessions of travel (during his stay). If he intends to stay there for four days or less, then he may avail himself of the concessions of travel. If a traveller halts in a city and does not know when he will finish his business there and does not set a specific time for his stay, then he may avail himself of the concessions of travel even if he stays there for a long time. No differentiation is made between travel on land or sea. End quote.
It also says (8/109):
The basic principle is that the one who is actually travelling is the one who may avail himself of the concession allowing shortening of the four-rak‘ah prayers, because Allah, may He be exalted, says (interpretation of the meaning): “And when you travel throughout the land, there is no blame upon you for shortening the prayer…” [an-Nisaa’ 4:101]. And Ya‘laa ibn Umayyah said: I said to ‘Umar ibn al-Khattaab (may Allah be pleased with him): “And when you travel throughout the land, there is no blame upon you for shortening the prayer, [especially] if you fear that those who disbelieve may disrupt [or attack] you” [an-Nisaa’ 4:101]. He said: I wondered about what you are wondering about, so I asked the Messenger of Allah (blessings and peace of Allah be upon him) and he said: “It is a charity that Allah has granted you, so accept His charity.” Narrated by Muslim.
The one who stays in a place for four days and nights, or less, is regarded as coming under the same rulings as the one who is actually travelling, because it is proven in the hadith of Jaabir and Ibn ‘Abbaas (may Allah be pleased with them) that the Prophet (blessings and peace of Allah be upon him) came to Makkah on the morning of the fourth day of Dhu’l-Hijjah for the Farewell Pilgrimage, and he (blessings and peace of Allah be upon him) stayed there on the fourth, fifth, sixth and seventh of the month, and prayed Fajr in al-Abtah on the eighth day, and he shortened the prayers during these days, as he had already decided to stay there [during that period], as is well-known. So anyone who is a traveller and intends to stay in a place for the length of time that the Prophet (blessings and peace of Allah be upon him) stayed there, or less than that, may shorten the prayers; the one who intends to stay there for longer than that must offer the prayers in full, because he does not come under the same ruling as a traveller.
But if a person stays in a place for more than four days whilst travelling, without having previously decided how long his stay will be – rather he decided that when he has completed his business he will leave, such as one who stays in a place to fight in jihad against the enemy, or is detained by the authorities, or kept from travelling by sickness, for example, and he intends that when his jihad end with victory or peace deal, or when he is rid of whatever was detaining him of sickness, enemy strength, authorities, the presence of bandits, the need to sell some goods, and the like, he will leave – then he is regarded as a traveller, and he may shorten the four-rak‘ah prayers, even if he stays there for a long time, because it is proven that when he conquered Makkah, the Prophet (blessings and peace of Allah be upon him) stayed there for nineteen days, during which he shortened the prayers, and he stayed in Tabook for twenty days to fight the Christians, during which he led his Companions in shortened prayers, because he had not decided to stay for a certain amount of time; rather his intention was to leave once he had finished what he went there to do. End quote.
Based on that, so long as you intend to stay for more than four days, then you must offer the prayers in full once you reach that city. However, during your journey, when you are on the road travelling there or back again, then you may shorten your prayers.
And Allah knows best.