Normally Jupiter-Saturn joint impact during transit plays a huge role in manifesting events in our life. For an Astrologer, it is a great help in making many predictions during the year as their joint impact makes it more prominent to have a particular event getting manifested. I discussed this concept in detail here - http://astrosaxena.com/jijs1718.
But we are about to enter in a year long time period and I am sure that there will be many such times in future where Jupiter-Saturn won't jointly impact any particular house or planet. It is when Jupiter enters Scorpio in Oct, 2018 and Saturn remains in Sagittarius. From Oct, 2018 to Nov, 2019, there will be no apparent joint impact of Jupiter-Saturn during transits. So, can we say that for 1 year there will be no major event like relation/marriage, child birth, job, promotion etc for anyone in the world? It doesn't look like so. That means events also depend on other planets. It also means that Jupiter-Saturn may be impacting us jointly but it may not be very apparent but need minute analysis of charts. So, let's see how Jupiter-Saturn can still jointly impact us in any such transit in 2019 and onward as & when it may happen.
As per the nature of houses.
Impact on house and house lords.
impact on karakas.
Let's try to understand through all the points one after the other -
As per the nature of houses - So, both Jupiter & Saturn may not be impacting the same house but they are impacting nature of same house by being in succeeding houses. Saturn is going to be in Sagittarius and Jupiter will be in Scorpio, So, for Pisces ascendant, Saturn will be in 10th house/Sagittarius whereas Jupiter will be in 9th house/Scorpio. 10th house is house of Career and Work. 9th house is 12th from 10th house. So, 9th house represents loss of career, i.e. resignations, firings and lay-offs. So, in a way both Saturn and Jupiter are impacting career related matters. It is nothing but joint impact of Jupiter-Saturn. We can apply the same in any house. Like for Gemini ascendant, Saturn will be in 7th house/Sagittarius of relation bringing stress in marriage and at the same time Jupiter will be in 6th house/Scorpio of disputes and conflicts. So, both Jupiter-Saturn are indicating that relationships can be troublesome for Gemini ascendant people in 2019. This is one way to see joint impact of Jupiter-Saturn.
Impact on house and house lords - Now, another way of joint impact is when lords are getting impacted during transits. Like Saturn in Sagittarius aspects Moon and Moon also gets aspect of Jupiter. So, Moon got joint impact of Jupiter-Saturn. Likewise, Jupiter is in Scorpio and now if Saturn aspects/transits over Mars or Ketu, lords of Scorpio, then Scorpio sign and relevant house is getting joint impact of Saturn and Jupiter.
impact on karakas - Likewise, karakas are going to be very important in making predictions. Like, Saturn is in 5th house/Sagittarius of love/romance for Leo ascendants and if Jupiter is aspecting or transiting over Venus then Jupiter-Venus both are indicating towards love and relation. If Jupiter is transiting through 10th house of Career and Saturn impacts Sun, which is karaka of Career, then it shows a major event in career is possible. So, not only houses but we need to be aware of all the planets that are getting impact of Jupiter-Saturn during transit.
Jaimini Karakas - Also, karakas of Jaimini Astrology (http://astrosaxena.com/bija) are going to play an important part. Like, suppose Saturn is transiting through 4th house/Sagittarius of home & real estate for Virgo ascendant and Jupiter's aspect or transit is over Mercury. Now, Mercury is 1st house & 10th house lord and nowhere it is karaka of home or real estate. But if Mercury is Matru karaka for that person then it opens the door for dealing in real estate matters. Like this, Jaimini Karakas can be an important tool to see the joint impact of Jupiter-Saturn during transit.
Bhavat Bhavam - Last but not the least, concept of Bhavat Bhavam - https://www.astrosaxena.com/bbhavam will help in understanding the events in a better way. Like Saturn may be impacting a house and Jupiter may be impacting the Bhavat Bhavam or Bhavat Bhavam Lord of same house. So, this concept can also help us.
Conclusion - And of course, there are other planets and other tools & tricks to predict the probable dates of event but the transits of Jupiter-Saturn in 2019 along with other planets will test the ability of Astrologers to minutely observe the chart+dasha+transits to predict an event.
Hope this helps. Thanks,