I am trying to make incense of meditation, but do not have the feat maximise spell. Can I UMD this, to emulate the feat ?
If so, what would be the target number.
You don't need to use UMD for this. You can ignore any prerequisite (except the feat itself) by adding +5 to the spellcraft DC.
If you don't have maximize spell but you do have access to Bless, the craft DC would be 5 + 7 + 5 = 17.
Note that all items have prerequisites in their descriptions. These prerequisites must be met for the item to be created. Most of the time, they take the form of spells that must be known by the item's creator (although access through another magic item or spellcaster is allowed). The DC to create a magic item increases by 5 for each prerequisite the caster does not meet. The only exception to this is the requisite item creation feat, which is mandatory. In addition, you cannot create potions, spell-trigger, or spell-completion magic items without meeting its prerequisites.
"You can use this skill to read a spell or to activate a magic item. Use Magic Device lets you use a magic item as if you had the spell ability or class features of another class, as if you were a different race, or as if you were of a different alignment."
So, the answer is no, Use Magic Device canNOT be used to emulate a feat to craft an item.
On the bright side, as Kudaku said, you do not need to worry about that as long as you increase the DC for every requirement that you do not meet, other than the craft feat itself.